JP2011247725A - Sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor element which is highly accurate and durable against the repetition of a regenerating operation and is capable of uniform temperature rise.SOLUTION: The sensor element includes: a sensor substrate 11A comprising ceramics having a first surface 13 and a second surface 15; a sensing electrode 17 disposed on the first surface 13 of the sensor substrate 11A and composed of a pair of electrodes 17a and 17b; and a heating conductor 19 disposed on the second surface 15 of the sensor substrate 11A and capable of heating the sensor substrate 11A. Then, for the sensor element 100A, the ratio of the surface roughness of at least a part where the sensing electrode 17 is disposed on the first surface 13 of the sensor substrate 11A to the thickness of the sensing electrode 17 is 0.2-4%, and the ratio of the surface roughness of at least a part where the heating conductor 19 is disposed on the second surface 15 of the sensor substrate 11A to the thickness of the heating conductor 19 is 1-3%.

Description

  The present invention relates to a sensor element, and more particularly to a sensor element that is highly accurate, has durability against repeated regenerating operations, and uniformly increases the temperature during the regenerating operation.

  Conventionally, the amount (concentration) of suspended matter is measured by detecting changes in insulation resistance caused by changes in the amount of conductive material deposited between a pair of electrodes, for suspended matter present in an area. Sensor elements are known.

  As such sensor elements, specifically, sensors for detecting fluctuations in the transport amount of powder transport machines, sensors for detecting troubles in filter devices for industrial equipment and automobiles, under dust work Examples of the element used in the environment detection sensor used can be exemplified (for example, see Patent Document 1). Furthermore, a particle counter used mainly for measuring the cleanness of a clean room is also known.

JP-A-60-123757

  However, the particle counter is intended to be used in an environment where there are few suspended solids, such as in a clean room, so it should not be used in an environment where there are more suspended solids than in a clean room. It was not appropriate.

  The sensor includes a sensor substrate made of ceramics, a pair of electrodes disposed on one surface of the sensor substrate, and a heating conductor disposed on the other surface. is there. Such a sensor has a regeneration operation (operation of raising the temperature from room temperature to a high temperature (specifically, 400 to 900 ° C. and then returning it to room temperature) in order to burn and remove the suspended matter accumulated between the pair of electrodes. Sometimes done. Such a regeneration operation causes a large temperature difference in the sensor element, and the sensor element may be damaged due to the temperature difference. For this reason, the sensor element is required to have durability against repeated reproduction operations, but conventional sensor elements have not had sufficient durability. Specifically, measurement may become impossible by repeating the reproduction operation.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is high accuracy, durability against repeated reproduction operations, and reproduction operations. Provided is a sensor element that uniformly increases temperature in time.

  According to the present invention, the following sensor element is provided.

[1] A sensor substrate made of ceramics having a first surface and a second surface, a sensing electrode that is disposed on the first surface of the sensor substrate, and includes a pair of electrodes, and the sensor substrate A heating conductor disposed on the second surface and capable of heating the sensor substrate and the sensing electrode, and at least the sensing on the first surface of the sensor substrate with respect to the thickness of the sensing electrode. The ratio of the surface roughness of the portion where the electrode for electrode is disposed is 0.2 to 4%, and at least the heating conductor on the second surface of the sensor substrate is arranged with respect to the thickness of the heating conductor. A sensor element having a surface roughness ratio of 1 to 3%.

[2] The ratio of the surface roughness of the first surface of the sensor substrate to the thickness of the sensing electrode is 0.2 to 4%, and the sensor substrate has a thickness of the heating conductor. The sensor element according to [1], wherein the surface roughness ratio of the second surface is 1 to 3%.

[3] The sensor element according to [1] or [2], wherein the sensor substrate is made of at least one ceramic selected from the group consisting of aluminum oxide, mullite, and spinel.

[4] The sensor substrate has a flat plate shape having a front surface that is the first surface and a back surface that is the second surface, the sensing electrode is disposed on the front surface, and the heating substrate is disposed on the back surface. The sensor element according to any one of [1] to [3], wherein a conductor is disposed.

[5] The pair of electrodes include a measurement unit that measures a change in electrical characteristics therebetween, and the measurement unit is made of a platinum group. A sensor element according to any one of the above.

[6] The sensor element according to [5], wherein the measurement unit is made of platinum.

[7] The sensor element according to any one of [1] to [6], further including an insulating layer that covers at least a part of the surface of the heating conductor.

  The sensor element of the present invention includes a sensor substrate made of ceramics having a first surface and a second surface, a sensing electrode made of a pair of electrodes, disposed on the first surface of the sensor substrate, and a sensor substrate. A heating conductor disposed on the second surface and capable of heating the sensor substrate and the sensing electrode, wherein at least the sensing electrode is disposed on the first surface of the sensor substrate with respect to the thickness of the sensing electrode. The ratio of the surface roughness of the surface portion of the second portion of the sensor substrate to the thickness of the heating conductor with respect to the thickness of the heating conductor is 0.2 to 4%. However, since it is 1 to 3%, it is highly accurate, has durability against repeating the regenerating operation, and increases the temperature uniformly during the regenerating operation.

It is a perspective view showing typically one embodiment of the sensor element of the present invention. It is sectional drawing which shows the AA cross section shown in FIG. It is sectional drawing which shows typically one Embodiment of the sensor element of this invention. It is sectional drawing which shows typically other embodiment of the sensor element of this invention. It is sectional drawing which shows typically reproduction | regeneration operation in one Embodiment of the sensor element of this invention. It is sectional drawing which shows typically reproduction | regeneration operation in one Embodiment of the sensor element of this invention. It is sectional drawing which shows typically reproduction | regeneration operation in one Embodiment of the sensor element of this invention.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and based on ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that modifications, improvements, and the like appropriately added to the embodiments described above fall within the scope of the present invention.

[1] Sensor element:
FIG. 1 is a perspective view schematically showing one embodiment of the sensor element of the present invention, and FIG. 2 is a cross-sectional view showing the AA cross section shown in FIG. As shown in FIGS. 1 and 2, the sensor element 100A of the present embodiment is arranged on a sensor substrate 11A made of ceramics having a first surface 13 and a second surface 15, and on the first surface 13 of the sensor substrate 11A. And a sensing electrode 17 having at least a pair of electrodes 17a and 17b, and a heating conductor 19 disposed on the second surface 15 of the sensor substrate 11A and capable of heating the sensor substrate 11A. Yes. In the sensor element 100A, the ratio of the surface roughness of at least the portion where the sensing electrode 17 is disposed on the first surface 13 of the sensor substrate 11A to the thickness of the sensing electrode 17 is 0.2 to 4%. The ratio of the surface roughness of at least the portion of the second surface 15 of the sensor substrate 11A where the heating conductor 19 is disposed to the thickness of the heating conductor 19 is 1 to 3%.

  In such a sensor element 100A, the ratio of the surface roughness of at least the portion where the sensing electrode 17 is disposed on the first surface 13 of the sensor substrate 11A to the thickness of the sensing electrode 17 is 0.2-4. Since the ratio of the surface roughness of at least the portion where the heating conductor 19 is disposed on the second surface 15 of the sensor substrate 11A to the thickness of the heating conductor 19 is 1 to 3%, Accuracy (that is, the pattern accuracy of the sensing electrode can be increased, the measurement accuracy is good, and the repeatability is good), and it has durability against repeated reproduction operations. Specifically, even if the regeneration operation is repeated, the sensing electrode and the heating conductor are difficult to separate from the sensor substrate.

  As described above, the sensor element of the present invention is regenerated by setting at least a part of the first surface of the sensor substrate and at least a part of the second surface to an appropriate surface state so as to satisfy a predetermined condition. Durable against repeated operations. And it becomes possible to raise temperature uniformly at the time of reproduction | regeneration operation. Specifically, during the regenerating operation, the sensor substrate 11A is uniformly heated by the heating conductor 19, and the sensing electrode 17 is uniformly heated by the uniformly heated sensor substrate 11A. is there.

  The sensor element 100A measures a change in electrical characteristics caused by the floating substance 21 (see FIG. 5B) deposited between the pair of electrodes 17a and 17b of the sensing electrode 17, thereby measuring the pair of electrodes. It is used for a sensor capable of measuring the concentration of the suspended matter 21 deposited between 17a and 17b. Specifically, the change in electrical characteristics means a change such as a change in insulation resistance (value) and a change in capacitance. As a method for measuring the concentration of the suspended matter 21, specifically, a calibration curve is prepared in advance based on the insulation resistance value between the pair of electrodes 17a and 17b of the sensing electrode 17 and the mass of the deposited suspended matter. In addition, from the insulation resistance value obtained when the sensor element is placed in a predetermined environment, the mass of the accumulated suspended matter can be calculated using the created calibration curve, and then converted into a concentration. . As described above, since the sensor element of the present invention measures a change in electrical characteristics, the sensor element is not limited to the property of the suspended matter to be measured (for example, conductivity or insulation), The amount or concentration of suspended solids can be measured with high accuracy. Furthermore, the accumulated floating substance is easy to use because it can be removed at any time by heating the sensor substrate and the sensing electrode with a heating conductor.

[1-1] Sensor substrate:
The sensor substrate is preferably made of at least one ceramic selected from the group consisting of aluminum oxide, spinel, and mullite. Among the ceramics, aluminum oxide is preferable because it has a good balance of thermal expansion coefficient, thermal conductivity, and high temperature strength.

  The surface roughness of each of the first surface and the second surface of the sensor substrate is not particularly limited as long as the relationship between the thickness of the sensing electrode and the thickness of the heating conductor satisfies the above conditions. The surface roughness of the portion where the heating conductor is disposed is preferably 0.01 to 1 μm, and more preferably 0.01 to 0.6 μm.

  Here, “surface roughness” in this specification is a value measured in accordance with JIS B 0601-1982, and means centerline average roughness.

  In order to finish the front and back surfaces of the sensor substrate to a desired roughness (surface roughness (surface roughness)), a blast method, a lapping method, a grinding method, and the like can be given. On the other hand, instead of post-processing, it is also possible to select the particle size of the ceramic powder used for the sensor substrate.

  Examples of a method for forming a surface with a surface roughness of 1 to 10 μm include a blasting method and a method for polishing the surface of the sensor substrate with a rough lapping (GC abrasive grains). Furthermore, as a method of forming a surface with a surface roughness of 0.04 to 0.1 μm, for example, after forming a surface with a surface roughness of 1 to 10 μm as described above, Examples thereof include a lapping method using diamond free abrasive grains (1 μm) and a method of polishing the surface of the sensor substrate using a # 1500 grinding wheel. In order to finish the surface roughness of 0.1 to 1 μm, the size of the abrasive grains used and the count of the grindstone may be changed. In addition, in order to finish only the portion where the sensing electrode and the heating conductor are provided to a desired surface roughness, a mask (that is, a mask having an inverted shape) that has a positive relationship with the electrode pattern is used. It is desirable to finish using a blasting method, particularly a wet blasting method. Since a slurry in which fine particles are dispersed can be used, the surface treatment uniformity and controllability are excellent and suitable for this application.

  The size of the sensor substrate is not particularly limited, but a size that is in the range of about 5 to 100 mm in length, 5 to 10 mm in width, and about 1 to 2 mm in thickness is preferable. This is a case where the outer shape is rectangular, but the shape can be freely selected according to the application.

[1-2] Sensing electrode:
In the sensing electrode, a voltage or the like is applied to a pair of electrodes of the sensing electrode, that is, electrodes (positive electrode and negative electrode) adjacent to each other with positive and negative potentials. And since the volume between a pair of electrodes of a sensing electrode influences the amount of detection of a suspended | floating matter, it is preferable that it is a thing with a high aspect ratio as a sensing electrode. However, when the aspect ratio is high, due to the high aspect ratio, sagging or blurring of the sensing electrode may occur and the distance between the pair of sensing electrodes may partially fluctuate. It was. Thus, if the distance between a pair of electrodes (positive electrode and negative electrode) of the sensing electrode varies (that is, the pattern accuracy is poor), there arises a problem that measurement is not stable between individual sensor elements. Therefore, in order to suppress the occurrence of such problems, devising the properties of the printing ink (conductor paste) that forms the sensing electrode, and printing ink that forms a rectangular cross section of the sensing electrode to be formed There was a need to develop.

  Here, when used at room temperature, by devising the properties of the printing ink (conductor paste), the above problem can be solved and an electrode having a desired shape can be formed. However, in a sensor element that repeatedly performs a regenerating operation, a temperature cycle is periodically performed from normal temperature to high temperature (specifically, 400 to 900 ° C.) and from high temperature to normal temperature. It receives a different load. Therefore, defects such as peeling or disconnection of the sensing electrode may occur.

  Therefore, the present inventors have examined the causal relationship between the surface roughness of the sensor substrate and the characteristics of the sensor element (specifically, the adhesion between the sensor substrate and the heating conductor) for conventional sensor elements. However, effective results were not obtained. That is, the characteristics of the sensor element may not be sufficiently improved only by defining the surface roughness of the sensor substrate. In other words, even if attention is paid to the surface roughness of the sensor substrate, the characteristics of the sensor element may not be sufficiently improved by simply changing the surface roughness to make the sensor substrate smooth or rough. It was. Therefore, instead of simply defining the absolute value of the surface roughness of the sensor board, the sensor board surface roughness and the sensing are arranged considering the interaction with the sensing electrode as in the sensor element of the present invention. It was examined to define the relationship with the electrode thickness. It has been found that the above characteristics are improved by conducting such studies.

  The present inventors devise the properties of the printing ink (adjust the rheology of the printing ink) in order to improve the pattern accuracy (that is, to make the aspect ratio high and the cross section rectangular). It has been found that the above problem can be solved by the relationship between the thickness of the sensing electrode and the surface roughness of the sensor substrate. Specifically, the measurement accuracy is improved by setting the ratio of the surface roughness of the surface of the sensor substrate on the side where the sensing electrode is disposed to the thickness of the sensing electrode within the predetermined range. In addition, it has been found that even when a load caused by a temperature cycle is applied during the regenerating operation, defects such as electrode peeling and disconnection hardly occur and a stable sensor element can be obtained. In addition, this application does not deny devising the property of printing ink.

  As described above, in the sensor element of the present invention, the ratio of the surface roughness of at least the portion where the sensing electrode is disposed on the first surface of the sensor substrate to the thickness of the sensing electrode is 0.2-4. %, Preferably 0.2 to 2.0%, more preferably 0.2 to 1.0%. When the ratio is less than 0.2%, the portion where the sensing electrode is disposed on the first surface of the sensor substrate is too smooth. Therefore, when forming the electrode for sensing by screen printing described later at the time of electrode formation, the electrode pattern is missing due to repelling printing ink (part of the sensing electrode to be formed is missing) Or peeling (the sensing electrode peels off easily). Further, the sensing electrode may be peeled off during firing or use. On the other hand, if it exceeds 4%, when the electrode for sensing is formed by screen printing, which will be described later, at the time of electrode formation, problems such as bleeding of the electrode pattern, lowering of pattern accuracy, and variation of the film thickness occur.

  The sensor element of the present invention is not particularly limited as long as the ratio of the surface roughness of at least the portion where the sensing electrode is disposed on the first surface of the sensor substrate to the thickness of the sensing electrode satisfies the above condition. . That is, the portion (only) where the sensing electrode is disposed may satisfy the above surface roughness ratio, or in addition to the portion where the sensing electrode is disposed, the sensing electrode is disposed. The part other than the part (specifically, the entire first surface (entire surface) of the sensor substrate) may also satisfy the ratio of the surface roughness.

  FIG. 3 is a cross-sectional view schematically showing one embodiment of the sensor element of the present invention. The sensor substrate 11A shown in FIG. 3 is an example showing an aspect in which the entire first surface 13 (entire surface) is finished to a desired surface roughness. The sensor element 100A including such a sensor substrate 11A has good shape accuracy, that is, stable characteristics, regardless of the thickness of the sensing electrode as long as the above conditions are satisfied. 3 to 5 are exaggerated to show the roughness of the surface.

  FIG. 4 is a cross-sectional view schematically showing another embodiment of the sensor element of the present invention. The sensor element 100B shown in FIG. 4 is an example showing that only the portion where the sensing electrode 17 is disposed on the first surface 13 is a surface satisfying the ratio of the surface roughness. As shown in FIG. 4, the manufacturing is facilitated because only the portion where the sensing electrode 17 is disposed is a surface satisfying the ratio of the surface roughness. In addition, since the processing stress of the sensor substrate can be minimized, environmental performance such as thermal shock is advantageous. In FIG. 4, the portion of the first surface 13 where the pair of electrodes 17a and 17b is not provided is drawn in a planar manner, but it is not necessarily a flat surface.

  The sensing electrode is a part (sensor part) that detects floating substances such as raw material powder, dust in the atmosphere, and soot in the exhaust gas at the manufacturing site. That is, as described above, when the floating substance 21 (see FIG. 5B) is deposited between the pair of electrodes 17a and 17b of the sensing electrode 17, the electrical characteristics (for example, capacitance) between the sensing electrodes 17a and 17b. , Insulation resistance value) changes. At this time, the floating substance may be conductive or insulating. As a pair of electrodes of such a sensing electrode, a known configuration capable of detecting a target substance (floating substance) can be adopted. For example, two comb-shaped electrodes are connected to comb teeth. And the like (see FIG. 2). The distance between the comb teeth (see symbol “d” in FIG. 2) can be determined as appropriate depending on the type of suspended matter, but is preferably 50 to 200 μm, and preferably 50 to 150 μm. More preferably. In addition, when the distance according to a measuring object (suspended substance) is not set, intended information (accurate measurement value) may not be obtained.

  Examples of the material for the sensing electrode include platinum groups such as platinum, rhodium, palladium and iridium, and metal materials having heat resistance such as tungsten and molybdenum. Among these, the platinum group is preferable, and in particular, platinum It is preferable that the material has as a main component.

  It is preferable that the pair of electrodes of the sensing electrode have a measurement unit (for example, the above-described comb-like portion) in which a change in electrical characteristics between them is measured. The measuring part is preferably made of a platinum group such as platinum, rhodium, palladium, iridium or the like, and more preferably made of platinum, iridium, or a mixture thereof. Thus, if the measurement part is made of a platinum group, the reactivity between the measurement part and suspended solids is low, and furthermore, it is not easily corroded by the use environment and has heat resistance that can withstand high temperatures during the regeneration operation. Therefore, it can be used even in a high temperature atmosphere (high temperature during the regenerating operation). Furthermore, when it is made of platinum, there is an advantage that it is particularly resistant to oxidation and has good workability.

  The thickness of the sensing electrode is not particularly limited, and is preferably, for example, 5 to 20 μm, and more preferably 10 to 20 μm. If the thickness is less than 5 μm, the reproducible cycle is shortened and the measurement error may be increased because the storage capacity of the suspended matter is small. On the other hand, if it exceeds 20 μm, it becomes difficult to keep the distance between the pair of electrodes of the sensing electrode constant, and the stress applied to the sensing electrode and the heating conductor may increase and may be easily peeled off. . The “thickness of the sensing electrode” means the thickness of each of a pair of sensing electrodes (usually a positive electrode and a negative electrode). Therefore, “the ratio of the surface roughness of at least the portion where the sensing electrode is disposed on the first surface of the sensor substrate to the thickness of the sensing electrode” is the thickness D1, each of the electrodes 17a and 17b. D2 (see FIG. 2) is the ratio of the surface roughness (see FIG. 2) at least on the portion of the first surface 13 of the sensor substrate 11A where the sensing electrodes are disposed, and is represented by the formula: {((sensor substrate 11A of the first surface 13 of 11A / the thickness D1 of the electrode 17a) + (the surface roughness of the first surface 13 of the sensor substrate 11A / the thickness D2 of the electrode 17b)) / 2} × 100. Value. The thicknesses D1 and D2 are usually the same.

  Examples of the shape of each electrode (positive electrode and negative electrode) of the sensing electrode include, for example, a spiral shape in addition to the above-described shape including a comb-tooth shape and a comb-tooth-shaped portion. In addition, the size of the sensing electrode (area occupied with respect to the entire first surface) can be appropriately determined according to the application and shape of the sensor element. Note that a plurality of pairs of sensing electrodes may be provided.

[1-3] Heating conductor:
The heating conductor is a member that can heat the sensor substrate and the sensing electrode (that is, the sensor substrate can be heated, and the sensing electrode can be heated through heating the sensor substrate). Then, by heating the sensor substrate and the sensing electrode, the suspended matter deposited between the pair of electrodes 17a and 17b of the sensing electrode 17 is burnt or decomposed and removed (see FIGS. 5B and 5C). ). This heating conductor heats the sensor substrate as appropriate, and does not function (does not heat) in principle when measuring suspended substances. However, depending on the usage environment, when the sensor element is condensed, it may be operated at a low temperature below the removal temperature. The heating temperature by the heating conductor is preferably 400 to 900 ° C., although it varies depending on the type of suspended substance measured.

  Further, the inventors of the present invention, for the conventional sensor element, the surface roughness of the sensor substrate and the characteristics of the sensor element (specifically, two-dimensional resistance uniformity, adhesion between the sensor substrate and the heating conductor) Although the causal relationship was investigated, effective results were not obtained. That is, the characteristics of the sensor element may not be sufficiently improved only by defining the surface roughness of the sensor substrate. In other words, even if attention is paid to the surface roughness of the sensor substrate, the characteristics of the sensor element may not be sufficiently improved by simply changing the surface roughness to make the sensor substrate smooth or rough. It was. Therefore, rather than simply defining the absolute value of the surface roughness of the sensor substrate, the surface roughness of the sensor substrate and the heating provided by taking into account the interaction with the heating conductor as in the sensor element of the present invention. It was examined to define the relationship with the conductor thickness. It has been found that the above-mentioned identification is improved by conducting such studies.

  Therefore, the present inventors do not devise the properties of the printing ink as in the case of the sensing electrode (adjust the rheology of the printing ink), but the thickness of the heating conductor and the surface roughness of the sensor substrate. It has been found that the above problem can be solved by the relationship. In addition, this application does not deny devising the property of printing ink.

  As described above, in the sensor element of the present invention, the ratio of the surface roughness of at least the portion where the heating conductor is disposed on the second surface of the sensor substrate to the thickness of the heating conductor is 1 to 3%. It is necessary to be 1 to 2%. When the ratio is less than 1%, there is a problem that the heating conductor is peeled off from the sensor substrate when the heating conductor is formed, when the laminated body is fired, or when the sensor element is used. On the other hand, if it exceeds 3%, the electrode pattern is likely to be lost, and the thickness of the heating conductor varies, so that the sensor element does not easily generate heat during the reproduction operation. Therefore, the obtained sensor element has a defect such as inferior reliability.

  And the sensor element of this invention does not have a restriction | limiting in particular, as long as the ratio of the surface roughness of the part by which at least the heating conductor is arrange | positioned in the 2nd surface of a sensor substrate satisfy | fills the said conditions. That is, the portion (only) where the heating conductor is disposed may satisfy the above-mentioned surface roughness ratio, or the heating conductor is disposed in addition to the portion where the heating conductor is disposed. Parts other than the above parts (specifically, the entire second surface (entire surface) of the sensor substrate) may also satisfy the ratio of the surface roughness.

  The sensor substrate 11A shown in FIG. 3 is an example showing that the entire second surface 15 (entire surface) is in a desired surface state. The sensor element 100A including such a sensor substrate 11A has good shape accuracy, that is, stable characteristics regardless of the wiring thickness.

  5A to 5C are cross-sectional views schematically showing a reproduction operation in one embodiment of the sensor element of the present invention. FIG. 5A shows the sensor element 100A in a state before measurement of suspended solids. When the sensor element is arranged in an atmosphere where the suspended matter is desired to be measured, the suspended matter 21 is deposited between the pair of electrodes 17a and 17b of the sensing electrode 17 of the sensor element 100A as shown in FIG. 5B. At this time, since the electrical characteristics between the pair of electrodes 17a and 17b of the sensing electrode 17 change, the amount and concentration of the suspended matter 21 can be calculated based on the amount of change. Then, after the measurement, as shown in FIG. 5C, the temperature of the heating conductor 19 is raised to heat the sensor substrate 11A. FIG. 5C shows a state in which the heating conductor 19 is heated to burn and decompose and remove the suspended matter 21. A plurality of heating conductors may be provided.

  Examples of the material for the heating conductor include a platinum group such as platinum, palladium and iridium, and a heat-resistant base metal material such as tungsten and molybdenum. Among these, platinum that does not oxidize is preferable when the sensor element is used in the air, and tungsten and molybdenum are preferable when used in a non-oxidizing atmosphere or embedded inside.

  The thickness of the heating conductor can be appropriately set depending on the material constituting the heating conductor, but is preferably 1 to 4 μm, and more preferably 1 to 2 μm, for example.

  The heating conductor has a shape that generates heat in a pattern (that is, a shape formed in a predetermined pattern including a curve, specifically, a conductor formed in a wave shape as shown in FIG. 1 and FIG. It may be a shape obtained by being bent and arranged so as to be U-turned at the tip portion of the surface, or may be a shape that generates heat on the surface (that is, for example, a film shape (planar shape)). The size (area occupied with respect to the entire surface of the second surface) and position of the conductor are not particularly limited and can be determined as appropriate, but the sensing electrode is positioned at a position corresponding to the portion where the sensing electrode is disposed. It is preferable that it is arrange | positioned by the area more than the part by which this was arrange | positioned.

[1-4] Insulating layer:
The sensor element of the present invention preferably further comprises an insulating layer covering at least a part of the surface of the heating conductor. By providing the insulating layer in this manner, the heating conductor can be protected even in an atmosphere such as exhaust gas, and therefore a heating conductor made of an inexpensive base metal can be used. Furthermore, short-circuiting and disconnection during use of the sensor can be suppressed, and if the material having the same thermal expansion coefficient as the thermal expansion coefficient of the sensor substrate is used as the insulating layer, the sensor element will warp when the regeneration operation generates heat or It is possible to suppress damage.

  Examples of the material for the insulating layer include glass, ceramics, and composites thereof. Among these, glass and ceramics are preferable from the viewpoint of excellent durability and manufacturing accuracy, and ceramics having the same quality as the sensor substrate or glass having the same thermal expansion coefficient as the sensor substrate is preferable.

  Although there is no restriction | limiting in particular in the thickness of an insulating layer, It is preferable that it is 5-40 micrometers, and it is still more preferable that it is 5-20 micrometers. When the thickness is less than 5 μm, the mechanical strength tends to be small, and therefore breakage tends to occur. On the other hand, if it exceeds 40 μm, since the mass is too large, the electric power required for heating in the regeneration operation increases, and the power efficiency tends to decrease.

  FIG. 2 is an example showing a sensor element 100 </ b> A further including an insulating layer 23 that covers the surface of the heating conductor 19. The sensor element 100A shown in FIG. 1 is drawn with the insulating layer omitted.

[2] Manufacturing method of sensor element:
As a manufacturing method of one embodiment of the sensor element of the present invention, a plurality of sheet-like green bodies are produced, a laminate is produced by laminating the produced sheet-like green bodies, and the produced laminate is fired. A fired body manufacturing step for obtaining a fired body, and a sensor element manufacturing step for obtaining a sensor element by disposing a sensing electrode on the first surface of the fired body and a heating conductor on the second surface. A method comprising: In addition, when a desired thickness as a sensor element can be ensured, only one sheet-like green body is used without producing a laminated body, and both sides of the one sheet-like green body are used for sensing. It is also possible to produce a sensor element by disposing an electrode and a heating conductor (another embodiment). Hereinafter, the manufacturing method of one embodiment of the sensor element of the present invention will be described more specifically.

  At least one ceramic raw material selected from the group consisting of aluminum oxide, spinel, and mullite is mixed with other components used as a forming raw material to prepare a slurry-like forming raw material. As the ceramic raw material, the above raw materials are preferable, but not limited thereto. As other raw materials, it is preferable to use a binder, a plasticizer, a dispersant, a dispersion medium and the like.

  The binder is not particularly limited, and may be either an aqueous binder or a non-aqueous binder. As the aqueous binder, a methyl cellulose resin, a polyvinyl alcohol resin, polyethylene oxide, an acrylic resin, or the like can be suitably used. As the non-aqueous binder, an ethyl cellulose resin, a polyvinyl butyral resin, an acrylic resin, or the like can be preferably used. Examples of the acrylic resin include (meth) acrylic resin, (meth) acrylic acid ester copolymer, acrylic acid ester-methacrylic acid ester copolymer, and the like.

  Although the addition amount of a binder is based also on the specific surface area of a ceramic raw material, it is preferable that it is about 4-20 mass parts with respect to 100 mass parts, and it is still more preferable that it is 6-15 mass parts. By setting it as such binder content, it becomes possible to prevent generation | occurrence | production of a crack etc., when shape | molding a slurry-like shaping | molding raw material and shape | molding a green sheet, and when drying and baking.

  As the plasticizer, glycerin, polyethylene glycol, dibutyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, or the like can be used.

  It is preferable that the addition amount of a plasticizer is 30-70 mass parts with respect to 100 mass parts of binder addition amounts. When the amount is more than 70 parts by mass, the green sheet becomes too soft and may be easily deformed in the process of processing the sheet. When the amount is less than 30 parts by mass, the green sheet becomes too hard and cracks are generated only by bending. Handling characteristics may deteriorate.

  As the dispersant, anionic surfactants, nonionic surfactants, and the like can be used in aqueous systems, and fatty acids, phosphate esters, sorbitan acid esters, synthetic surfactants, and the like can be used in non-aqueous systems. .

  It is preferable that a dispersing agent is 1-5 mass parts with respect to 100 mass parts of ceramic raw materials.

  As the dispersion medium, water or the like can be used. The amount of the dispersion medium used can be set as appropriate.

  Each of the above raw materials is sufficiently mixed and kneaded using an alumina pot or a trommel containing alumina boulders to produce a slurry-like forming raw material for producing a sheet-like green body.

  Next, the obtained slurry-like forming raw material for producing the sheet-like green body is stirred under reduced pressure to defoam, and further prepared to have a predetermined viscosity. The viscosity of the slurry-like forming raw material obtained in the preparation of the forming raw material is preferably 500 to 20000 mPa · s, and more preferably 2000 to 10,000 mPa · s. It is preferable to adjust the viscosity range in this manner because the slurry can be easily formed into a sheet shape. If the slurry viscosity is too high or too low, molding may be difficult. The viscosity of the slurry is a value measured with a B-type viscometer.

  Next, the slurry-like forming raw material obtained by the above method is formed into a sheet shape to form a sheet-like green body. The forming method is not particularly limited as long as the forming raw material can be formed into a sheet shape to form a sheet-like green body, and a known method such as a doctor blade method, a calender roll method, a thermal gelation method, or a casting is used. can do. Moreover, dry manufacturing methods, such as a roll compaction method, are employable. The thickness of the sheet-like green body to be manufactured is preferably 50 to 300 μm.

  Next, a sheet-like green body is laminated to obtain a laminate. When laminating a sheet-like green body, it is preferable to carry out pressure while heating.

  The obtained laminate is dried at 50 to 120 ° C. and fired at a desired temperature to obtain a fired body. In addition, when a sheet-like green body contains an organic binder, it is preferable to degrease at 400-600 degreeC before baking.

  Next, for the obtained fired body, a predetermined portion of the front surface and the back surface (at least the sensing electrode on the first surface (front surface) of the sensor substrate, and the thickness of the heating conductor, The sensor substrate is finished to a desired roughness (surface roughness (surface roughness)) at least on the second surface (back surface) of the sensor substrate where the heating conductor is disposed. As the method, a method such as the blast method described above can be appropriately employed.

  Next, a sensing electrode and a heating conductor are disposed on the first surface (front surface) and the second surface (back surface) of the fired body obtained. As a method for disposing the sensing electrode and the heating conductor, a method such as screen printing can be employed. When arranging the sensing electrode and the heating conductor by screen printing, specifically, first, a conductor paste for forming the sensing electrode and the heating conductor is prepared. This conductor paste contains at least one selected from the group consisting of gold, silver, platinum group, nickel, molybdenum, and tungsten in accordance with each material necessary for forming each of the sensing electrode and the heating conductor. It can be prepared by adding a solvent such as binder and terpineol to the powder and kneading using a triroll mill or the like. Next, the prepared conductor pastes are printed on the first surface (front surface) and the second surface (back surface) of the fired body using a screen printing method to form sensing electrodes and heating conductors having predetermined shapes. . In this way, the sensor element of the present invention can be produced.

  In order to accurately form the sensing electrode and the heating conductor, it is preferable to blow at least the surface of the conductor paste by blowing hot air immediately after each conductor paste is printed using a screen printing method or the like. Here, “immediately after printing” means 2 to 10 seconds after printing, and preferably 2 to 5 seconds after printing.

  As described above, after firing the laminate to obtain a fired body, the present invention is not limited to printing the conductor paste on the fired body, and the sensor element can be obtained by firing after printing the conductor paste on the laminate. It can also be produced. Moreover, in the method of forming the laminated body in this way, the heating conductor may be embedded in the laminated body. Furthermore, a part of the sensing electrode may be embedded in the laminate. When the heating conductor is embedded in the laminated body, there is an advantage that the heating conductor can be protected even in an atmosphere such as exhaust gas without further forming an insulating layer.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

Example 1
First, polyvinyl butyral as a binder, di-2-ethylhexyl phthalate as a plasticizer, sorbitan trioleate as a dispersant, an organic solvent (xylene, butanol = 6: 4 (mass ratio)) and alumina as a dispersion medium. These were put in an alumina pot and mixed to prepare a slurry-like forming raw material for producing a sheet-like green body. The amount of each raw material used was 6 parts by mass of binder, 3 parts by mass of plasticizer, 2 parts by mass of dispersant, and 35 parts by mass of organic solvent with respect to 100 parts by mass of alumina.

  Next, the obtained slurry-like forming raw material for producing the sheet-like green body was stirred under reduced pressure to defoam, and prepared to have a viscosity of 50000 mPa · s. The viscosity of the slurry was measured with a B-type viscometer.

  Next, the slurry-like forming raw material obtained by the above method was formed into a sheet using a doctor blade method to produce a green sheet having a thickness of 250 μm.

  Four similar green sheets (thickness 250 μm) were stacked on the surface of the obtained green sheet, and five green sheets were laminated. Thereafter, pressure lamination and thermocompression bonding were performed using a heatable uniaxial press to obtain a flat laminate having a thickness of about 1.25 mm having a front surface and a back surface. Thereafter, the obtained laminate was fired at 1600 ° C. for 2 hours to obtain a fired body. The surface roughness (surface roughness) of the fired body was 0.35 μm on both the front and back surfaces.

  Next, in order to obtain a predetermined surface roughness, the surface and the back surface of the obtained fired body were processed. Specifically, it was finished with a lapping with diamond abrasive grains until the surface roughness was 0.2 μm, and finished with a rough lapping with GC abrasive grains until the surface roughness was 0.8 μm. The surface roughness was measured with a stylus having a tip diameter of 2 μm using a surface roughness meter manufactured by Rank Taylor Hobson.

  Next, a sensing electrode and a heating conductor as shown in FIGS. 1 and 2 were disposed on the surface (first surface) and the back surface (second surface) of the fired body having a predetermined surface roughness. Specifically, first, a conductor paste for forming a sensing electrode and a heating conductor was prepared as follows. Di-ethylene glycol / monobutyl ether / acetate as a solvent, ethyl cellulose as a binder, and polyethylene glycol monooleate as a dispersant were added to platinum powder as a conductor and kneaded using a tri-roll mill (in terms of mass ratio, conductor: solvent : Binder: Dispersant = 90: 5: 4: 1). In this way, a conductor paste was prepared.

  Next, the prepared conductor paste was printed on the surface (first surface) and back surface (second surface) of the fired body using a screen printing method. And immediately after printing the said conductor paste and obtaining a to-be-printed material (for 2 to 10 seconds after printing), the surface and back surface of this to-be-printed material were immediately dried with the hot air of 80 degreeC, and were further baked at 1200 degreeC. . In this way, a sensor element having a sensing electrode on the front surface and a heating conductor on the back surface as shown in FIGS. 1 and 2 was obtained.

  The obtained sensor element was a flat bar shape of length 70 mm × width 6 mm × thickness 1 mm, and the heating conductor was sized to fit within an area of length 6 mm × width 5 mm. The thickness of the heating conductor was 4 μm, and the thickness of the sensing electrode was 15 μm. And the sensor element of a present Example is 0.2% (refer Table 3), if the ratio of the surface roughness in the surface (1st surface) of a sensor board | substrate with respect to the thickness of the electrode for sensing is 0.2%, see heating When the ratio of the surface roughness on the back surface (second surface) of the sensor substrate to the thickness of the conductor for use was calculated, it was 1.0% (see Tables 1 and 2).

  The produced sensor element was subjected to “reliability evaluation”, “temperature variation evaluation”, and “resistance value variation evaluation” by the following methods.

[Reliability evaluation method]
An operation of heating the sensor element at room temperature to 900 ° C. and then cooling it to room temperature is performed as one cycle, and is repeated 1000 cycles. Then, it evaluates by observing visually. The evaluation criterion is a case where peeling of the sensing electrode and the heating conductor is not confirmed, and a case where peeling of the sensing electrode and the heating conductor is confirmed is rejected. Moreover, the case where the pass result was obtained 10 times or more was set as “A”, and the case where the pass result was less than 10 times was set as “B”. The results are shown in the “Evaluation” column. In addition, 1000 cycles of operation were performed 10 times. The measurement results and evaluation results are shown in Table 1. In Table 1, “surface roughness (μm)” indicates the surface roughness of the second surface of the sensor substrate, and “ratio (%)” indicates the second of the sensor substrate relative to the thickness of the heating conductor. The ratio of the surface roughness of the surface is shown.

[Temperature variation evaluation method]
The temperature of the first surface of the sensor substrate when the heating conductor is set to 900 ° C. is measured with a thermometer ((model number) “TVS-200EX” manufactured by Nippon Avionics). The temperature measurement is performed by measuring the temperature at any 10 locations. Table 2 shows the measurement temperature, average temperature, and standard deviation (σ). The temperature variation is evaluated from the standard deviation (σ) value. A case where the standard deviation (σ) is small (specifically, 15 ° C. or less) is “A”, and a case where the standard deviation (σ) is large (specifically, a case where it exceeds 15 ° C.) is “B”. It was. The results are shown in the “Evaluation” column. Table 2 shows the measurement results and the evaluation results. Note that the heating conductor was peeled off from the sensor substrate in a portion that did not reach the set temperature (900 ° C.) of the heating conductor. In Table 2, “surface roughness (μm)” indicates the surface roughness of the second surface of the sensor substrate, and “ratio (%)” indicates the thickness of the second surface of the sensor substrate with respect to the thickness of the heating conductor. The ratio of surface roughness is shown.

[Evaluation method of resistance variation]
After repeating 1000 cycles similarly to [Reliability evaluation method], the conduction resistance value of the positive electrode of the pair of sensing electrodes (positive electrode and negative electrode) is measured with an LCR meter. In addition, 1000 cycles of operation were performed 10 times. The case where the variation of the resistance value was 0.1Ω or less was regarded as a pass “A”, and the case where the resistance value was more than 0.1Ω was regarded as a disapproval “B”. The results are shown in the “Evaluation” column. Table 3 shows the measurement results and the evaluation results. In Table 3, “-” indicates that the electrode was peeled off, and the standard deviation was satisfied (0.1Ω or less), but was rejected as “B”. In Table 3, “surface roughness (μm)” indicates the surface roughness of the first surface of the sensor substrate, and “ratio (%)” indicates the ratio of the first surface of the sensor substrate to the electrode thickness. The ratio of surface roughness is shown.

(Examples 2 and 3, Comparative Examples 1 and 2)
The sensor elements of Examples 2 and 3 and Comparative Examples 1 and 2 were produced in the same manner as in Example 1 except that the surface roughness (μm) shown in Table 1 was used. Thereafter, as in the case of Example 1, “reliability evaluation”, “temperature variation evaluation”, and “resistance value variation evaluation” were performed on each sensor element produced in the same manner as in Example 1. The results are shown in Tables 1 to 3.

  As is clear from Tables 1 to 3, the sensor elements of Examples 1 to 3 can be more durable and have a uniform temperature increase than the sensor elements of Comparative Examples 1 and 2 with respect to repeated regeneration operations. I was able to confirm.

  In Examples 1 and 2, since the ratio of the surface roughness of the sensor substrate was more appropriate, the result of “evaluation of temperature variation” was good. In Example 3, the “temperature variation evaluation” result is “A” evaluation, but the standard deviation is large. Such a large standard deviation indicates that the ratio of the surface roughness of the sensor substrate is greatly involved in the relationship between the electrode thickness and the temperature variation. Specifically, it is estimated that the film quality of the electrode is deteriorated.

  In Comparative Example 1, the degree of peeling of the sensing electrode and the heating conductor was large, and the result of “reliability evaluation” was deteriorated.

  The sensor element of the present invention can be used as a sensor for measuring the concentration of suspended solids, and specifically, can be suitably used as a sensor installed in an exhaust system of an automobile or the like.

11A, 11B: sensor substrate, 13: first surface, 15: second surface, 17: sensing electrode, 17a, 17b: electrode, 19: heating conductor, 21: floating substance, 23: insulating layer, 100A, 100B : Sensor element.

Claims (7)

A sensor substrate made of ceramics having a first surface and a second surface;
A sensing electrode disposed on the first surface of the sensor substrate and including a pair of electrodes;
A heating conductor disposed on the second surface of the sensor substrate and capable of heating the sensor substrate and the sensing electrode;
The ratio of the surface roughness of at least the portion where the sensing electrode is disposed on the first surface of the sensor substrate to the thickness of the sensing electrode is 0.2 to 4%,
A sensor element in which a ratio of surface roughness of at least a portion of the second surface of the sensor substrate on which the heating conductor is disposed to a thickness of the heating conductor is 1 to 3%.   The ratio of the surface roughness of the first surface of the sensor substrate to the thickness of the sensing electrode is 0.2 to 4%, and the second of the sensor substrate with respect to the thickness of the heating conductor. The sensor element according to claim 1, wherein the surface roughness ratio of the surface is 1 to 3%.   The sensor element according to claim 1, wherein the sensor substrate is made of at least one ceramic selected from the group consisting of aluminum oxide, mullite, and spinel. The sensor substrate is a flat plate having a front surface that is the first surface and a back surface that is the second surface;
The sensor element according to claim 1, wherein the sensing electrode is disposed on the front surface, and the heating conductor is disposed on the back surface.   The said pair of electrodes have a measurement part by which the change of the electrical property between them is measured, The said measurement part consists of a platinum group, As described in any one of Claims 1-4. Sensor element.   The sensor element according to claim 5, wherein the measurement unit is made of platinum.   The sensor element as described in any one of Claims 1-6 further equipped with the insulating layer which coat | covers at least one part of the surface of the said conductor for a heating.

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