Gas sensor element

Abstract

Provided is a gas sensor element in which a gap is less likely to occur between an inner wall surface of a through-hole formed in a ceramic layer and a blank in contact with the inner wall surface. The gas sensor element includes a heat generating portion and a ceramic layer. The ceramic layer has a first surface and a second surface on an opposite side of the first surface, and is heated by the heat generating portion. The ceramic layer has a through-hole that penetrates the ceramic layer in a thickness direction from the first surface toward the second surface, and constitutes a via hole for electrically connecting the first surface side and the second surface side. The through-hole is defined by a first inner wall surface extending in the thickness direction and a second inner wall surface that is continuous with the first inner wall surface and defines a recessed portion that is recessed more toward an inner side of the ceramic layer than the first inner wall surface. When the thickness of the ceramic layer is 1, the length of the first inner wall surface from a position closest to a central axis of the through-hole to a position farthest into the recessed portion is 0.05 or more and 0.20 or less.

Description

Technical Field

[0001] This invention relates to gas sensor elements. Background Technology

[0002] Conventionally, gas sensors are known for measuring the gaseous components in gases such as automobile exhaust. These gas sensors have a gas sensor element comprising, for example, multiple stacked ceramic layers and a detection section formed on one side along its length. In such gas sensor elements, a heater layer including a heating element is formed between the ceramic layers. Furthermore, conductive portions such as the energized terminals of the heating element and monitoring electrodes are sometimes sandwiched between one or more ceramic layers and disposed on one side and the other. Therefore, through holes are formed in the ceramic layers for electrically connecting these conductive portions along their entire thickness.

[0003] Patent Document 1 discloses a gas sensor element comprising: a first ceramic layer having a first through-hole, and a second ceramic layer stacked on the first ceramic layer having a second through-hole. In this gas sensor element, a first conductor portion is formed on the inner peripheral surface of the first through-hole, and a second conductor portion is formed on the inner peripheral surface of the second through-hole, achieving electrical contact between the first and second conductor portions. Patent Document 2 discloses a gas sensor element comprising a ceramic sheet having a through-hole penetrating both a surface and a back surface, and having a conductive pattern that allows electrical conduction between the surface and the back surface. In this gas sensor element, an insulating paste is printed on the inner wall surface of the through-hole, and a conductive paste is printed on the insulating paste to achieve electrical connection between the surface and the back surface.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2008-046112

[0007] Patent Document 2: Japanese Patent No. 4421756 Summary of the Invention

[0008] Gas sensor elements with the configuration disclosed in Patent Document 1 sometimes have a gap between the inner circumferential surface of the through-hole and the conductor portion. If liquid components such as moisture present in this gap move through the heater layer to the heating element and its vicinity, they evaporate into water vapor due to the heat of the heating element, causing a local pressure increase. Consequently, peeling sometimes occurs within the internal structure of the gas sensor element, leading to damage to the gas sensor element. This also applies to gas sensor elements with the configuration disclosed in Patent Document 2. That is, liquid components present between the inner circumferential surface of the through-hole and the insulating paste move through the insulating paste and heater layer to the heating element and its vicinity, where they evaporate as the ambient temperature rises, causing a local pressure increase, which may lead to the same peeling. In such cases, when the ceramic forming the inner circumferential surface of the through-hole and the material of the component printed on the inner circumferential surface or filling the through-hole are different, a gap may form between them, allowing peeling moisture to enter and potentially causing damage to the gas sensor element.

[0009] One aspect of the present invention is implemented in view of the above circumstances, and its object is to provide a gas sensor element in which gaps are not easily generated between the inner wall surface of the through hole formed in the ceramic layer and the blank in contact with the inner wall surface.

[0010] The present invention employs the following configuration to solve the aforementioned problems.

[0011] The gas sensor element according to the first aspect of the present invention includes a heating element and a ceramic layer. The ceramic layer is configured to have a first surface and a second surface located opposite to the first surface, and is heated by the heating element. The ceramic layer has a through-hole extending through the ceramic layer along its thickness direction from the first surface toward the second surface, forming a through-hole for electrically connecting the first surface side and the second surface side. The through-hole is defined by a first inner wall surface extending along the thickness direction and a second inner wall surface continuous with the first inner wall surface and defining a recess that is recessed further inward than the first inner wall surface into the ceramic layer. When the thickness of the ceramic layer is set to 1, the length of the first inner wall surface from the position closest to the central axis of the through-hole to the innermost position of the recess is 0.05 or more and 0.20 or less.

[0012] According to the first viewpoint, a recess is formed in the through hole for penetrating the ceramic layer along the thickness direction, recessed towards the inside of the ceramic layer. Furthermore, the maximum depth of the recess, based on the position closest to the central axis of the through hole, is 0.05 to 0.15 units relative to the thickness of the ceramic layer. Accordingly, when forming a through hole using a ceramic layer and different materials, the adhesion between the first and second inner wall surfaces of the ceramic defining the through hole and the different materials is improved, and gaps are less likely to form between them.

[0013] Based on the gas sensor element of the first aspect of the present invention, when the thickness of the ceramic layer is set to 1, the length of the first inner wall surface from the position closest to the central axis of the through hole to the innermost position of the recess is 0.10 or more and 0.20 or less.

[0014] The gas sensor element according to the third aspect of the present invention is based on the gas sensor element according to the first or second aspect, wherein the second inner wall surface is continuous over the entire circumference of the through hole, and the recess is defined by the second inner wall surface as being annular when viewed from the first surface side.

[0015] According to the third viewpoint, the recess is formed as a continuous portion around the central axis of the through hole. This allows for further improvement in the adhesion between the ceramic and different materials.

[0016] The gas sensor element according to the fourth aspect of the present invention is based on the gas sensor element according to any one of the first to third aspects, wherein the second inner wall surface exists in the thickness direction at at least one of a position biased towards the first surface side and a position biased towards the second surface side.

[0017] The gas sensor element according to the fifth aspect of the present invention is based on the gas sensor element according to any one of the first to fourth aspects, wherein the second inner wall surface has a plurality of components along the thickness direction.

[0018] The gas sensor element according to the sixth aspect of the present invention, based on the gas sensor element according to any one of the first to fifth aspects, further includes a conductive portion, which is conductive and formed to fill the interior of the through hole.

[0019] The gas sensor element according to the seventh aspect of the present invention is based on the gas sensor element according to any one of the first to sixth aspects, wherein the heating element is disposed on the first surface side of the ceramic layer, and the through hole electrically connects the heating element and the elements on the second surface side of the ceramic layer.

[0020] The gas sensor element according to the eighth aspect of the present invention is configured, based on the gas sensor elements according to any one of the first to seventh aspects, to measure the concentration of nitrogen oxides in the gas to be measured.

[0021] Invention Effects

[0022] According to the present invention, a gas sensor element can be provided in which gaps are not easily generated between the inner wall surface of the through hole formed in the ceramic layer and the different materials in contact with the inner wall surface, thereby making the internal structure less prone to peeling. Attached Figure Description

[0023] Figure 1 It is a cross-sectional schematic diagram that summarizes the configuration of a sensor element involved in one embodiment.

[0024] Figure 2 This is a schematic diagram showing an example of a planar configuration of the heating element and its surrounding area.

[0025] Figure 3 This is another schematic diagram showing a general planar configuration of the heating element and its surroundings.

[0026] Figure 4 This is a partial cross-sectional view of the conductive portion involved in one embodiment.

[0027] Figure 5 This is a partial cross-sectional view of the periphery of a through hole in one embodiment.

[0028] Figure 6 This is a partial cross-sectional view of the periphery of the through hole according to another embodiment.

[0029] Figure 7A This is a partial cross-sectional view of the periphery of the through hole involved in the modified example.

[0030] Figure 7B This is a partial cross-sectional view of the periphery of the through hole involved in the modified example.

[0031] Figure 7C This is a partial cross-sectional view of the periphery of the through hole involved in the modified example.

[0032] Figure 7D This is a partial cross-sectional view of the periphery of the through hole involved in the modified example.

[0033] Figure 7E This is a partial cross-sectional view of the periphery of the through hole involved in the modified example.

[0034] Figure 8 This is a partial cross-sectional view of the periphery of the through hole involved in the comparative example.

[0035] Explanation of reference numerals in the attached figures

[0036] 100…Gas sensor element, 4…First solid electrolyte layer, 6…Second solid electrolyte layer, 5…Isolation layer, 7…Gas flow section (internal space), 11…First diffusion rate control section (diffusion rate control unit), 13…Second diffusion rate control section (diffusion rate control unit), 30…Third diffusion rate control section (diffusion rate control unit), 16…Fourth diffusion rate control section (diffusion rate control unit), 20…First internal cavity, 40…Second internal cavity (Cavity), 17…Third internal cavity, 72…Heating part, 73…Conductive part, 74…Heater insulation layer, 200…Upper surface (first surface), 201…Lower surface (second surface), 202…Upper surface (first surface), 203…Lower surface (second surface), 210…Upper first inner wall surface, 211…Lower first inner wall surface, 212…(Upper) second inner wall surface, 220…Recess, A1…Central shaft, H1…Through hole, H2…Through hole, P1…Conductive part. Detailed Implementation

[0037] Hereinafter, based on the accompanying drawings, an embodiment of one aspect of the present invention (hereinafter also referred to as "this embodiment") will be described. However, the embodiment described below is merely an example of the present invention in all respects. Various modifications and variations can be made without departing from the scope of the present invention. That is, when implementing the present invention, specific configurations corresponding to the embodiments can be appropriately adopted. It should be noted that the constituent elements shown in the figures are sometimes represented in a modified manner for ease of explanation and do not necessarily represent the actual size relationship of each constituent element.

[0038] <1. Composition of Gas Sensor Elements>

[0039] Figure 1 This is a cross-sectional schematic diagram illustrating an example of the configuration of the gas sensor element 100 according to this embodiment. The gas sensor element 100 is, for example, an elongated strip-shaped body extending along the length direction, or, for example, formed into a cuboid shape. Figure 1 The illustrated gas sensor element 100 has a front end and a rear end as each end in the length direction. In the following description, the front end will be referred to as... Figure 1 The left end, and the rear end is set as Figure 1 The right end. Additionally, as... Figure 1 As shown, the direction facing inwards from the front of the paper is defined as the left-right direction of the gas sensor element 100. However, the shape of the gas sensor element 100 is not limited to this example, and can be appropriately selected according to the embodiment. Furthermore, the orientation of the gas sensor element 100 during use is not limited to... Figure 1 The orientation specified in the text.

[0040] The gas sensor element 100 comprises six layers: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, an insulating layer 5, and a second solid electrolyte layer 6, all constructed using solid electrolyte layers. Figure 1 The cross-sectional view shows the structure obtained by stacking layers in this order starting from the bottom. That is, the gas sensor element 100 has a laminate composed of a first solid electrolyte layer 4, a second solid electrolyte layer 6, and an isolation layer 5. The solid electrolyte forming the six layers—first substrate layer 1, second substrate layer 2, third substrate layer 3, first solid electrolyte layer 4, isolation layer 5, and second solid electrolyte layer 6—can be a dense solid electrolyte. Dense means having a porosity of 5% or less.

[0041] The gas sensor element 100 is manufactured by, for example, performing predetermined processing and wiring pattern printing processes on ceramic green sheets corresponding to each layer, then stacking them, and finally firing them to achieve integration. As an example, the gas sensor element 100 is a stack of multiple ceramic layers. Hereinafter, layers 1 to 6 will sometimes be referred to as "ceramic layers" without distinction. In this embodiment, the upper surface of the second solid electrolyte layer 6 constitutes the upper surface of the gas sensor element 100, the lower surface of the first substrate layer 1 constitutes the lower surface of the gas sensor element 100, and each side surface of each layer 1 to 6 constitutes each side surface of the gas sensor element 100.

[0042] [Gas Flow Section Being Measured]

[0043] On the front end side of the gas sensor element 100, between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, a gas inlet 10, a first diffusion rate control unit 11, a buffer space 12, a second diffusion rate control unit 13, a first internal cavity 20, a third diffusion rate control unit 30, a second internal cavity 40, a fourth diffusion rate control unit 16, and a third internal cavity 17 are formed adjacent to each other in a sequentially connected manner.

[0044] The gas inlet 10, buffer space 12, first internal cavity 20, second internal cavity 40 and third internal cavity 17 are spaces (internal spaces) inside the gas sensor element 100, which are provided by hollowing out the isolation layer 5. The upper part of the space is divided by the lower surface of the second solid electrolyte layer 6 and the lower part is divided by the upper surface of the first solid electrolyte layer 4.

[0045] The first diffusion velocity control unit 11 is configured as two horizontally elongated slits (the direction perpendicular to the drawing is the direction of the long side of the opening). In addition, the second diffusion velocity control unit 13, the third diffusion velocity control unit 30, and the fourth diffusion velocity control unit 16 are respectively configured as holes whose lengths extending in the direction perpendicular to the drawing are shorter than those of the first internal cavity 20, the second internal cavity 40, and the third internal cavity 17.

[0046] like Figure 1 As illustrated, the second diffusion rate control unit 13, the third diffusion rate control unit 30, and the fourth diffusion rate control unit 16 can all be configured as two horizontally elongated slits (the direction perpendicular to the drawing is the direction of the long side of the opening) similar to the first diffusion rate control unit 11, but are not limited thereto. For example, the fourth diffusion rate control unit 16 can be configured as a single horizontally elongated slit (the direction perpendicular to the drawing is the length direction of the opening) formed as a gap between itself and the lower surface of the second solid electrolyte layer 6. That is, the fourth diffusion rate control unit 16 can contact the upper surface of the first solid electrolyte layer 4. The second diffusion rate control unit 13, the third diffusion rate control unit 30, and the fourth diffusion rate control unit 16 will be described separately below. The portion (internal space) from the gas inlet 10 to the third internal cavity 17 is referred to as the measured gas flow section 7.

[0047] [Reference Gas Import Space]

[0048] A reference gas inlet space 43 is provided at a position farther from the front end side than the gas flow section 7, between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and at a position defined by the side of the first solid electrolyte layer 4. For example, a reference gas such as air is introduced into the reference gas inlet space 43. However, the configuration of the gas sensor element 100 is not limited to this example. As another example, the first solid electrolyte layer 4 may be configured to extend to the rear end of the gas sensor element 100, and the reference gas inlet space 43 may be omitted. In this case, the atmospheric inlet layer 48 may be configured to extend to the rear end of the gas sensor element 100.

[0049] [Atmospheric entry layer]

[0050] The atmosphere introduction layer 48 is constructed of porous alumina, through which reference gas is introduced via the reference gas introduction space 43. Furthermore, the atmosphere introduction layer 48 is configured to cover the reference electrode 42.

[0051] [Reference Electrode]

[0052] The reference electrode 42 is formed as follows: it is sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and an atmospheric inlet layer 48 connected to the aforementioned reference gas inlet space 43 is disposed around it. The reference electrode 42 is used to measure the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 17. Details will be described below.

[0053] [Gas Inlet]

[0054] The gas inlet 10 is an opening in the gas flow section 7 relative to the external space. The gas to be measured is introduced into the gas sensor element 100 from the external space through the gas inlet 10. In this embodiment, as... Figure 1 As illustrated, the gas inlet 10 is disposed on the front surface of the gas sensor element 100. That is, the gas to be measured flow section 7 is configured to have an opening at the front end of the gas sensor element 100. However, it is not necessary for the gas to be measured flow section 7 to have an opening on the front surface of the gas sensor element 100, i.e., for the gas inlet 10 to be disposed on the front surface of the gas sensor element 100. As long as the gas sensor element 100 can introduce the gas to be measured from the external space into the interior of the gas to be measured flow section 7, the gas inlet 10 can be disposed, for example, on the right side or left side of the gas sensor element 100.

[0055] When the gas inlet 10 is disposed on the front surface of the gas sensor element 100, the gas flow section 7 to be measured on each side (right and left sides) of the gas sensor element 100 can be sealed by a dense ceramic layer. The ceramic layer can be made of a material such as zirconium oxide (ZrO2). When the gas flow section 7 to be measured is sealed on each side of the gas sensor element 100 by a dense ceramic layer, the gas sensor element 100 is configured such that the gas to be measured is introduced into the gas sensor element 100 from the external space through the gas inlet 10.

[0056] However, regarding the gas sensor element 100, it is not necessary for the gas to be measured to flow through the gas flow section 7 on each side of the gas sensor element 100 to be sealed with a dense ceramic layer. Furthermore, it is not necessary for the gas sensor element 100 to have a gas inlet 10. That is, the gas sensor element 100 only needs to be able to introduce the gas to be measured from the external space into the interior of the gas flow section 7; it is not necessary for the gas to be measured to be introduced from the external space through the gas inlet 10. For example, for the gas sensor element 100, at least one side of the insulating layer 5 can be left open instead of being sealed with a dense ceramic layer, thus allowing the gas to be measured to be introduced from the external space into the interior of the gas flow section 7 without providing a gas inlet 10.

[0057] [First Diffusion Velocity Control Unit]

[0058] The first diffusion rate control unit 11 is a part that applies a predetermined diffusion resistance to the gas to be measured introduced from the gas inlet 10.

[0059] [Buffer Space]

[0060] The buffer space 12 is a space provided for guiding the measured gas introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13.

[0061] [Second Diffusion Rate Control Unit]

[0062] The second diffusion rate control unit 13 is a part that applies a predetermined diffusion resistance to the gas being measured introduced from the buffer space 12 into the first internal cavity 20.

[0063] When the gas to be measured is introduced from outside the gas sensor element 100 into the first internal cavity 20, it is rapidly introduced into the gas sensor element 100 from the gas inlet 10 due to pressure fluctuations in the external space (pulsations in exhaust pressure in the case of automobile exhaust). The gas is not directly introduced into the first internal cavity 20, but rather after the concentration fluctuations are eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Therefore, the concentration fluctuation of the gas introduced into the first internal space becomes almost negligible.

[0064] [First internal cavity]

[0065] The first internal cavity 20 is configured as a space for adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the second diffusion rate control unit 13. The main pump unit 21 operates to adjust this oxygen partial pressure.

[0066] [Main Pump Unit]

[0067] The main pump unit 21 is an electrochemical pump unit consisting of an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched between the inner pump electrode 22 and the outer pump electrode 23. The inner pump electrode 22 has a top electrode portion 22a disposed on the almost entire surface of the lower surface 62 of the second solid electrolyte layer 6, adjacent to (facing) the first internal cavity 20. The outer pump electrode 23 is disposed on the upper surface 63 of the second solid electrolyte layer 6 in a region corresponding to the top electrode portion 22a, in a manner adjacent to the external space.

[0068] The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (second solid electrolyte layer 6 and first solid electrolyte layer 4) that divide the first internal cavity 20, and the isolation layer 5 that forms the sidewalls. Specifically, a top electrode portion 22a is formed on the lower surface 62 of the second solid electrolyte layer 6 that forms the top surface of the first internal cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that forms the bottom surface. Furthermore, side electrode portions (not shown) are formed on the sidewall surfaces (inner surfaces) of the isolation layer 5 that forms the two sidewall portions of the first internal cavity 20 in a manner connected to the top electrode portion 22a and the bottom electrode portion 22b. That is, the inner pump electrode 22 is disposed in a tunnel-shaped structure at the location of the side electrode portion.

[0069] The inner pump electrode 22 and the outer pump electrode 23 are formed as porous metal-ceramic electrodes (e.g., metal-ceramic electrodes composed of Pt and ZrO2 containing 1% Au). It should be noted that the inner pump electrode 22, which is in contact with the gas being measured, utilizes a method to reduce the impact of nitrogen oxides (NOx) in the gas being measured. x It is formed from materials with reducing power of components.

[0070] The gas sensor element 100 is configured such that: in the main pump unit 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in a positive or negative direction, thereby enabling oxygen in the first internal cavity 20 to be drawn out to the external space, or oxygen in the external space to be drawn into the first internal cavity 20.

[0071] [Oxygen partial pressure detection sensor unit for main pump control]

[0072] In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an oxygen partial pressure detection sensor unit 80 for main pump control (i.e., an electrochemical sensor unit) is formed by the inner pump electrode 22, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

[0073] The gas sensor element 100 is configured such that by measuring the electromotive force V0 of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) within the first internal cavity 20 can be determined. Furthermore, feedback control is applied to Vp0 to keep the electromotive force V0 constant, thereby controlling the pump current Ip0. Thus, the oxygen concentration within the first internal cavity 20 can be maintained at a predetermined constant value.

[0074] [Third Diffusion Rate Control Unit]

[0075] The third diffusion rate control unit 30 is a component that applies a predetermined diffusion resistance to the gas to be measured after the oxygen concentration (oxygen partial pressure) has been controlled in the first internal cavity 20 by the operation of the main pump unit 21, and introduces the gas to be measured into the second internal cavity 40.

[0076] [Second internal cavity]

[0077] The second internal cavity 40 is configured as a space for further adjusting the oxygen partial pressure in the gas to be measured, which is introduced through the third diffusion rate control unit 30. This oxygen partial pressure is adjusted by operating the auxiliary pump unit 50.

[0078] [Auxiliary Pump Unit]

[0079] The auxiliary pump unit 50 is an auxiliary electrochemical pump unit consisting of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, but any suitable electrode on the outside of the gas sensor element 100), and a second solid electrolyte layer 6. The auxiliary pump electrode 51 has a top electrode portion 51a that is provided almost entirely on the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

[0080] The auxiliary pump electrode 51 is disposed in the second internal cavity 40 with the same tunnel-shaped structure as the inner pump electrode 22 previously disposed in the first internal cavity 20. Specifically, a top electrode portion 51a is formed relative to the lower surface 62 of the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, and a bottom electrode portion 51b is formed on the upper surface of the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40. Furthermore, side electrode portions (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b are formed on the two wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40. Accordingly, the auxiliary pump electrode 51 has a tunnel-shaped structure.

[0081] It should be noted that the auxiliary pump electrode 51 is also formed using a material that reduces the reducing power of nitrogen oxide components in the measured gas, just like the inner pump electrode 22.

[0082] The gas sensor element 100 is configured such that a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23 in the auxiliary pump unit 50, thereby enabling oxygen in the atmosphere inside the second internal cavity 40 to be drawn out to the external space, or oxygen to be drawn from the external space into the second internal cavity 40.

[0083] [Oxygen partial pressure detection sensor unit for auxiliary pump control]

[0084] In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an auxiliary pump control oxygen partial pressure detection sensor unit 81 (i.e., an electrochemical sensor unit) is constructed from an auxiliary pump electrode 51, a reference electrode 42, a second solid electrolyte layer 6, an isolation layer 5, a first solid electrolyte layer 4, and a third substrate layer 3.

[0085] It should be noted that the auxiliary pump unit 50 utilizes a variable power supply 52 for pumping, which is voltage-controlled based on the electromotive force V1 detected by the oxygen partial pressure detection sensor unit 81 for auxiliary pump control. Thus, the oxygen partial pressure in the atmosphere within the second internal cavity 40 is controlled to a level substantially conducive to NO. x The measurement of the lower partial pressure has no effect.

[0086] Additionally, simultaneously, its pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor unit 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor unit 80 for main pump control, and its electromotive force V0 is controlled, thereby ensuring that the gradient of oxygen partial pressure in the gas to be measured, introduced from the third diffusion rate control unit 30 into the second internal cavity 40, remains constant. (The last sentence appears to be incomplete and possibly refers to a separate point about NO.) x When the sensor is in use, the oxygen concentration in the second internal cavity 40 is maintained at a constant value of about 0.001 ppm due to the action of the main pump unit 21 and the auxiliary pump unit 50.

[0087] [Fourth Diffusion Rate Control Unit]

[0088] The fourth diffusion rate control unit 16 is a part that applies a predetermined diffusion resistance to the gas to be measured after the oxygen concentration (oxygen partial pressure) has been controlled by the operation of the auxiliary pump unit 50 in the second internal cavity 40, and introduces the gas to be measured into the third internal cavity 17.

[0089] [Third internal cavity]

[0090] The third internal cavity 17 is configured as a space for performing the following process: processing nitrogen oxides (NOx) in the gas to be measured introduced through the fourth diffusion rate control unit 16. x The concentration of NO was measured. The NO concentration was determined by measuring the action of pump unit 41. x The concentration is measured. In this embodiment, within the second internal cavity 40, an auxiliary pump unit 50 is used to further adjust the oxygen partial pressure of the gas to be measured, which has been pre-adjusted in the first internal cavity 20 and then introduced through the third diffusion rate control unit 30. Accordingly, the oxygen concentration of the gas to be measured introduced from the second internal cavity 40 to the third internal cavity 17 can be kept constant with high precision. Therefore, the gas sensor element 100 according to this embodiment can measure NO with high precision.x concentration.

[0091] [Measurement Pump Unit]

[0092] The measuring pump unit 41 measures the concentration of nitrogen oxides in the gas to be measured within the third internal cavity 17. The measuring pump unit 41 is an electrochemical pump unit consisting of a measuring electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. Figure 1 In one example, the measuring electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4, adjacent to (facing) the third internal cavity 17.

[0093] [Measuring Electrode]

[0094] The measuring electrode 44 is a porous metal-ceramic electrode. The measuring electrode 44 also serves as a detector for NO present in the atmosphere within the third internal cavity 17. x NO to be reduced x It functions by reducing the catalyst. Figure 1 In one example, the measuring electrode 44 is exposed within the third internal cavity 17. In another example, the measuring electrode 44 may be covered by a diffusion rate control unit. This diffusion rate control unit may be constructed of a porous membrane primarily composed of alumina (Al2O3). This diffusion rate control unit is responsible for controlling the NO flowing into the measuring electrode 44. x It limits the amount of [something] and also acts as a protective film for measuring electrode 44.

[0095] The gas sensor element 100 is configured such that, in the measuring pump unit 41, oxygen generated by the decomposition of nitrogen oxides in the atmosphere surrounding the measuring electrode 44 can be drawn out, and its generation amount can be detected as pump current Ip2.

[0096] In addition, to detect the oxygen partial pressure around the measuring electrode 44, an oxygen partial pressure detection sensor unit 82 (i.e., an electrochemical sensor unit) for measuring pump control is constructed from the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. The variable power supply 46 is controlled based on the voltage (electromotive force) V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control.

[0097] The gas to be measured, introduced into the third internal cavity 17, reaches the measuring electrode 44 under controlled oxygen partial pressure. Nitrogen oxides in the gas around the measuring electrode 44 are reduced (2NO→N2+O2) to generate oxygen. This generated oxygen is pumped by the measuring pump unit 41. At this time, the voltage Vp2 of the variable power supply is controlled so that the control voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control remains constant. The amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas being measured; therefore, the concentration of nitrogen oxides in the gas being measured is calculated using the pump current Ip2 in the measuring pump unit 41.

[0098] Furthermore, by combining the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 to form an oxygen partial pressure detection mechanism as an electrochemical sensor unit, it is possible to detect the electromotive force corresponding to the following difference: the difference refers to the NO concentration in the atmosphere surrounding the measuring electrode 44. x The difference between the amount of oxygen generated by the reduction of the component and the amount of oxygen contained in the reference atmosphere can be used to determine the concentration of nitrogen oxides in the measured gas.

[0099] [Sensor Unit]

[0100] Furthermore, the electrochemical sensor unit 83 is composed of the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. The gas sensor element 100 is configured such that an electromotive force Vref can be obtained using the sensor unit 83, and the oxygen partial pressure in the gas to be measured outside the sensor can be detected using the electromotive force Vref.

[0101] In the gas sensor element 100 with the above-described configuration, by operating the main pump unit 21 and the auxiliary pump unit 50, the oxygen partial pressure can be maintained at a constant low value (essentially for NO). x The gas to be measured (without affecting the measured value) is supplied to the measuring pump unit 41. Therefore, the gas sensor element 100 is configured such that, based on the pump current Ip2, it can determine the concentration of nitrogen oxides in the gas to be measured, which is approximately proportional to the concentration of nitrogen oxides in the gas to be measured. x The oxygen generated by the reduction is drawn out by the measuring pump unit 41 and circulated.

[0102] [Heater]

[0103] In addition, the gas sensor element 100 includes a heater 70, which performs the function of heating and maintaining the temperature of the gas sensor element 100. The heater 70, in addition to the heater electrode 71 described later, is located in the thickness direction of the gas sensor element 100. Figure 1 The heater 70 is positioned closer to the lower surface of the gas sensor element 100 than the upper surface of the gas sensor element 100 in the vertical direction. However, the configuration of the heater 70 is not limited to this example and can be appropriately selected according to the implementation method.

[0104] The heater 70 mainly comprises: heater electrodes 71, heating elements 72 (72a, 72b), a conductive element 73, and a heater insulating layer 74. Additionally, Figure 1 In one example, the heater 70 also includes a pressure relief port 75. As described later, the conductive portion 73 is formed by a pair of through holes penetrating the first substrate layer 1 and the second substrate layer 2 along the thickness direction, so as to electrically connect the lower surface side of the first substrate layer 1 and the upper surface side of the second substrate layer 2 (see reference). Figure 2 , 3 ).

[0105] The heater electrode 71 is an electrode formed in contact with the lower surface of the first substrate layer 1 (the lower surface of the gas sensor element 100). By connecting the heater electrode 71 to an external power source, power can be supplied to the heating element 72 from the outside via the conductive part 73.

[0106] The heating element 72 is a resistive element formed by sandwiching the second substrate layer 2 and the third substrate layer 3, that is, a resistive heating element disposed between the second substrate layer 2 and the third substrate layer 3. It is powered by a heater power supply (not shown) provided outside the gas sensor element 100 through the heater electrode 71 and the conductive part 73, which serve as the power supply path, so that the heating element 72 heats up and heats and keeps the solid electrolyte forming the gas sensor element 100 warm.

[0107] The heating element 72 is formed of Pt, or is formed with Pt as the main component. The heating element 72 is embedded in a predetermined range on the side of the gas sensor element 100 where the gas to be measured flows 7 is located, opposite to the gas to be measured flow section 7 in the element thickness direction. The heating element 72 is provided to have a thickness of, for example, about 10 μm to 20 μm.

[0108] Figure 2 This is a schematic diagram showing an example of a general planar configuration of the heating element 72 and its surroundings. For example... Figure 2As shown, the heating element 72 has a serpentine portion 72a that snakes along the front side of the gas sensor element 100, and a pair of straight portions 72b that extend linearly from both ends of the serpentine portion 72a toward the rear end of the gas sensor element 100. It should be noted that the shape of the serpentine portion 72a is not limited to... Figure 2 For example, it could be... Figure 3 The shape shown. The pair of straight sections 72b are configured to have approximately the same shape, that is, the resistance values ​​of the two are the same. The rear ends of the straight sections 72b are connected to a pair of through holes that respectively constitute the conductive sections 73.

[0109] Furthermore, the heating element 72 can adjust the entire gas sensor element 100 to the temperature at which the solid electrolyte is activated. That is, in the gas sensor element 100, current flows through the heating element 72 via the heater electrode 71, causing the heating element 72 to heat up, thereby heating each part of the gas sensor element 100 to a predetermined temperature and maintaining that temperature. Specifically, the gas sensor element 100 is heated until the temperature of the solid electrolyte and electrode near the gas flow section 7 is, for example, around 700°C to 900°C (or 750°C to 950°C).

[0110] The heater insulating layer 74 is an insulating layer formed to cover the heating element 72. For example, it is an insulating layer formed on the upper and lower surfaces of the heating element 72 by an insulator such as alumina (Al2O3). The purpose of forming the heater insulating layer 74 is to obtain electrical insulation between the second substrate layer 2 and the heating element 72, and between the third substrate layer 3 and the heating element 72. The heater insulating layer 74 is provided with a thickness of about 70 μm to 110 μm at a distance of about 200 μm to 700 μm from the front end surface and side surface of the gas sensor element 100. However, the thickness of the heater insulating layer 74 does not need to be constant, and the locations where the heating element 72 is present and the locations where the heating element 72 is not present can be different.

[0111] The pressure relief hole 75 is a portion that penetrates the third substrate layer 3 and communicates with the reference gas introduction space 43. The purpose of forming the pressure relief hole 75 is to mitigate the increase in internal pressure that accompanies the temperature rise within the heater insulation layer 74. However, providing the pressure relief hole 75 is not mandatory, and it may be omitted.

[0112] [Through Hole]

[0113] Figure 4This is a partial cross-sectional view showing the configuration of the conductive portion 73 and its surroundings. In this embodiment, the conductive portion 73 is formed by electrically connecting the lower surface 203 side of the first substrate layer 1 and the upper surface 200 side of the second substrate layer 2, that is, by electrically connecting the lower surface 203 side and the upper surface 202 side of the first substrate layer 1, and the lower surface 201 side and the upper surface 200 side of the second substrate layer 2, respectively, but it is not limited to this. The through hole in this embodiment is composed of a through hole H1 penetrating the first substrate layer 1, a through hole H2 penetrating the second substrate layer 2, and a conductive portion P1 formed to fill the interior of the through holes H1 and H2. The through hole H1 penetrates the first substrate layer 1 along the thickness direction from the upper surface 202 towards the lower surface 203. The through hole H2 is configured to penetrate the second substrate layer 2 along the thickness direction from the upper surface 200 to the lower surface 201, and communicate with the through hole H1 when the first substrate layer 1 and the second substrate layer 2 are stacked.

[0114] The conductive portion P1 can be formed to fill the interior of the through-hole H1, and is continuously formed on the lower surface 203 of the first substrate layer 1 at the periphery defining the through-hole H1. Similarly, the conductive portion P1 can be formed to fill the interior of the through-hole H2, and is continuously formed on the upper surface 200 of the second substrate layer 2 at the periphery defining the through-hole H2. This makes the electrical connection between the heater electrode 71 and the pair of linear portions 72b of the heating portion 72 more reliable.

[0115] The conductive part P1 is obtained by firing a conductive paste with Pt as the main component together with a ceramic green sheet corresponding to the first substrate layer 1 and the second substrate layer 2, but it is not limited to this. That is, the conductive part P1 is integrally formed with the first substrate layer 1 and the second substrate layer 2. According to the inventor's research, because the conductive paste and the ceramic green sheet that will become the conductive part P1 have different shrinkage rates when they are heated and integrated, gaps often occur between the inner wall surface of the defined through holes H1 and H2 and the conductive part P1. Sometimes, liquid components such as moisture can enter into these gaps from the outside of the gas sensor element 100. As described above, the heater insulation layer 74 is a porous material such as alumina, so the infiltrated liquid components sometimes move inside and at the interface of the heater insulation layer 74 and reach the heating part 72 and its vicinity. When the ambient temperature rises as the heating part 72 heats up, the liquid components that reach the heating part 72 and its vicinity evaporate here and become water vapor, etc. As a result, the pressure locally increases, causing the internal structure of the gas sensor element 100, including the heater 70, to peel off, leading to damage to the gas sensor element 100.

[0116] The inventors conducted in-depth research and discovered that by improving the seal between the conductive portion P1 and the inner wall surface of the ceramic layer defining the through holes H1 and H2, liquid components are prevented from intruding, thus suppressing damage to the gas sensor element 100 caused by liquid component intrusion. Specifically, the inventors found that by forming at least one recess within a specified depth range on the inner wall surface of the defined through holes H1 and H2, the anchoring effect between the ceramic green sheet and the conductive paste can be improved. This configuration can be applied to both the first substrate layer 1 and the second substrate layer 2, or to at least one of them. The following description uses the second substrate layer 2 and the through hole H2 as an example. The upper surface 200 and lower surface 201 of the second substrate layer 2 are examples of the first and second surfaces of the present invention, respectively. It should be noted that the following description can also be applied to the first substrate layer 1 and the through hole H1, in which case the upper surface 202 and lower surface 203 of the first substrate layer 1 are examples of the first and second surfaces of the present invention, respectively.

[0117] Figure 5 This is a cross-sectional view near the through-hole H2 in the second substrate layer 2. As described above, the through-hole H2 penetrates the second substrate layer 2 along the thickness direction from the upper surface 200 to the lower surface 201. The shape of the through-hole H2 in the top view of the second substrate layer 2 is not particularly limited, and can be approximately circular, oblong, rectangular, etc. The axis passing through the geometric center of this shape and extending along the thickness direction of the second substrate layer 2 is defined as the central axis A1 of the through-hole H2.

[0118] Figure 5 In the example shown, the through-hole H2 is defined by an upper first inner wall surface 210, a second inner wall surface 212 continuous with the upper first inner wall surface 210, and a lower first inner wall surface 211. The upper first inner wall surface 210 and the lower first inner wall surface 211 are surfaces that extend approximately along the thickness direction of the second substrate layer 2. The upper first inner wall surface 210 is continuous with the upper surface 200, and the lower first inner wall surface 211 is continuous with the lower surface 201. The second inner wall surface 212 is a surface that is continuous with the upper first inner wall surface 210 at its upper end and with the lower first inner wall surface 211 at its lower end, and defines a recess 220 that is recessed further inward into the second substrate layer 2 than the upper first inner wall surface 210 and the lower first inner wall surface 211. In this embodiment, the second inner wall surface 212 is continuous in a constant shape at a constant position in the thickness direction of the second substrate layer 2 around the entire circumference of the through-hole H2. Therefore, in this embodiment, the recess 220 is defined by the second inner wall surface 212 as having a substantially constant depth over the entire circumference of the through hole H2 and being annular when viewed from above. However, the configuration of the second inner wall surface 212 is not limited to this; its shape may vary along the circumference of the through hole H2, or it may be discontinuous rather than continuous over the entire circumference of the through hole H2.

[0119] According to the inventors' research, when the thickness L1 of the second substrate layer 2 is set to 1, the anchoring effect is effectively achieved when the depth L2 to the innermost position of the recess 220 is 0.05 or more and 0.20 or less, and the anchoring effect is even more effectively achieved when the depth L2 is 0.10 or more and 0.20 or less. Here, the depth L2 to the innermost position of the recess 220 refers to the maximum depth of the recess 220 determined based on the position closest to the central axis A1 of the upper first inner wall surface 210 and the lower first inner wall surface 211 in a cross-section of the second substrate layer 2 including the central axis A1 and parallel to the length direction of the second substrate layer 2. The depth L2 relative to the thickness L1 is determined based on a cross-sectional photograph of the second substrate layer 2 taken using an electron microscope (manufactured by Hitachi Advanced Technology Co., Ltd., SU-1510). That is, in the above cross-sectional photograph, the distance between the position of the pixel determined to be closest to the central axis A1 on the upper first inner wall surface 210 and the lower first inner wall surface 211, and the position of the pixel determined to be furthest from the central axis A1 on the second inner wall surface 212, can be defined as the depth L2. On the other hand, regarding the thickness L1, in the above cross-sectional photograph, the distance along the thickness direction from the position of the pixel determined to be on the upper surface 200 to the position of the pixel determined to be on the lower surface 201 can be the average value of 10 randomly selected points.

[0120] By making the maximum depth of the recess 220 within the aforementioned range, the conductive paste used to form the conductive portion P1 can easily enter the recess 220. Furthermore, by utilizing the relative unevenness formed by the upper first inner wall surface 210, the second inner wall surface 212, and the lower first inner wall surface 211, an anchoring effect can be generated between the conductive paste and these wall surfaces, absorbing the shrinkage difference between the ceramic layer and the conductive paste.

[0121] For reasons explained later, it is preferable that one second inner wall surface 212 exists in the thickness direction of the second substrate layer 2, at a position biased towards either the upper surface 200 side or the lower surface 201 side, but this is not a limitation. That is, the second inner wall surface 212 can exist at any position in the thickness direction of the second substrate layer 2, except for positions continuous with the upper surface 200 and the lower surface 201. In addition, there can be two or more second inner wall surfaces 212 in the thickness direction. Furthermore, the shape of the second inner wall surface 212 (i.e., the shape of the recess 220) in the cross-sectional view of the second substrate layer 2 is not particularly limited and can be appropriately selected.

[0122] <2. Methods for forming through holes>

[0123] Hereinafter, an example of a method for manufacturing a gas sensor element 100, including the method for forming the through hole (conductive portion 73) according to this embodiment, will be described. However, the method for forming the conductive portion 73 and the method for manufacturing the gas sensor element 100 are not limited thereto.

[0124] First, ceramic green sheets are prepared to form the ceramic layers of the gas sensor element 100, based on the number of ceramic layers to be formed. That is, in this embodiment, six ceramic green sheets are prepared. As described above, the ceramic green sheets contain a solid electrolyte as a ceramic component. The thickness of these ceramic green sheets can be all the same, or it can vary depending on the layers to be formed.

[0125] Next, through holes for positioning during printing and lamination are formed on the six ceramic green sheets. For example, a punching device can be used to punch holes in the ceramic green sheets in the thickness direction to form through holes. Through holes H1 in the first substrate layer 1 and through holes H2 in the second substrate layer 2 for the conductive portion 73 can also be formed at this stage. For example, if the above-mentioned recess 220 is formed in the second substrate layer 2, a punching device can be used to form the upper first inner wall surface 210, the lower first inner wall surface 211, and the second inner wall surface 212 in one punching operation, thereby forming the through hole H2 and the recess 220 in one punching operation. Alternatively, after forming a through hole defined by an inner wall surface extending approximately parallel to the thickness direction using a punching device, a suitable portion of the inner wall surface can be removed to form the recess 220.

[0126] Next, the ceramic green sheet to be formed into the third substrate layer 3, the first solid electrolyte layer 4, the separator layer 5, and the second solid electrolyte layer 6 is subjected to printing and drying processes to obtain the desired pattern. For example, known methods such as screen printing can be used for printing. In addition, the drying process can also be performed using known methods.

[0127] Before, during, or simultaneously with the aforementioned printing and drying processes, conductive paste to be used as conductive portion P1 is filled into the through holes H1 of the ceramic green sheet to be the first substrate layer 1 and the through holes H2 of the ceramic green sheet to be the second substrate layer 2, respectively. At this time, if a recess 220 is present near the filling side, the conductive paste enters the recess 220 more reliably, thus further improving the adhesion between the conductive paste and the ceramic layer. This is the reason why it is preferable to have a second inner wall surface 212 at a position biased towards either the upper surface 200 side or the lower surface 201 side. This applies not only to the case where the second inner wall surface 212 is formed on the ceramic green sheet to be the second substrate layer 2, but also to the case where the second inner wall surface is formed on the ceramic green sheet to be the first substrate layer 1.

[0128] Before, during, or simultaneously with the aforementioned printing and drying processes, a heating element 72 and a heater insulation layer 74 are formed on the upper surface of the ceramic green sheet to be formed as the second substrate layer 2. The heating element 72 and heater insulation layer 74 can be formed by separately printing heater paste and insulating paste for forming the heating element 72 (72a, 72b) and drying them. More specifically, insulating paste is printed on the surface with a predetermined pattern and thickness and then dried. Next, heater paste is printed on the insulating paste with a predetermined pattern and thickness and then dried. Furthermore, insulating paste is printed on the heater paste with a predetermined pattern and thickness and then dried. For example, Pt paste and paste with Pt as the main component can be used as the heater paste; for example, a paste with Al2O3 as the main component can be used as the insulating paste.

[0129] After printing and drying patterns on six ceramic green sheets, they are positioned together and stacked in a prescribed order. They are then pressed together under specified temperature and pressure conditions to form a six-layer ceramic laminate. This laminate includes multiple unfired gas sensor elements 100. These elements are then cut and fired at a specified firing temperature to obtain individual gas sensor elements 100. In each gas sensor element 100, a conductive portion P1 is formed to fill the internal spaces of through holes H1 and H2, thus becoming a conductive portion 73.

[0130] <3. Characteristics>

[0131] According to the above embodiment, a simple method can be used to improve the adhesion between the inner wall surface of the through hole used to form the through hole and the conductive paste filled therein. This prevents gaps from forming between the ceramic layer and the conductive part, thereby suppressing the peeling of internal components of the gas sensor element 100 caused by the evaporation of the liquid components that have penetrated therein. Therefore, a gas sensor element 100 that is not easily broken can be provided.

[0132] <4. Variations>

[0133] The embodiments of the present invention have been described above; however, the foregoing description of the embodiments is merely an example of the present invention in all respects. Various modifications and variations can be made to the above embodiments. Regarding the constituent elements of the above embodiments, constituent elements can be omitted, substituted, or added as appropriate. Furthermore, the shape and size of the constituent elements of the above embodiments can be appropriately changed according to the embodiments. For example, the following changes can be made. It should be noted that, hereinafter, the same reference numerals are used for the same constituent elements as in the above embodiments, and descriptions of the same points as in the above embodiments are appropriately omitted. The following variations can be appropriately combined.

[0134] (1) The gas sensor element 100 of the above embodiment includes a first substrate layer 1; however, the first substrate layer 1 may be omitted, and the second substrate layer 2 may be configured as follows: Figure 1 The bottommost ceramic layer.

[0135] (2) The conductive paste filling the through holes H1 and H2 is not limited to the conductive paste described in the above embodiments. For example, such as Figure 6 As shown, the inner walls of the through holes H1 and H2 can be covered with insulating paste P2, and then the interior of the through holes H1 and H2 can be filled with conductive paste that becomes conductive part P1, thereby forming conductive part 73.

[0136] Even under the above circumstances, by forming a through-hole including a recess in at least one of the first substrate layer 1 and the second substrate layer 2, it is possible to prevent gaps from forming between the ceramic layer and the different material, namely the insulating paste P2. Therefore, it is possible to achieve the effect of avoiding peeling caused by the evaporation of liquid components. It should be noted that since the conductive paste and the insulating paste P2 have high adhesion, it is even more important to prevent gaps from forming between the ceramic layer and the parts formed of different materials that are in contact with the ceramic layer.

[0137] (3) The cross-sectional shape of the inner wall surface of the through hole H2 (H1) is not limited to the shape described in the above embodiment and can be appropriately modified. For example, the cross-sectional shape of the inner wall surface of the through hole H2 (H1) can be like... Figures 7A to 7E The shapes of the recesses 220, 220a, and 220b are defined in that way, and in all cases, the depth L2 can be determined in the same way as in the above-described embodiment. Figure 7A Yes: An example in which the recess 220, which has a cross-sectional shape substantially the same as that in the above embodiment, is formed on the lower surface side of the ceramic layer rather than on the upper surface side. Figure 7B This is an example where a recess 220a is formed on the upper surface side and a recess 220b is formed on the lower surface side of the ceramic layer. In this case, the recess 220a can be defined using the upper second inner wall surface 212 and the recess 220b can be defined using the lower second inner wall surface 214. Alternatively, a first inner wall surface that is continuous at both ends with the upper second inner wall surface 212 and the lower second inner wall surface 214 can be designated as an intermediate first inner wall surface 213.

[0138] Figures 7C to 7E These are examples of recesses 220 with other cross-sectional shapes. The second inner wall surface 212 can be as follows: Figure 7C In the cross-sectional view shown, it is concave and convex in shape. Furthermore, the cross-sectional shape of the recess 220 is not only a shape with corners, but can also be as follows: Figure 7D The shape is smoothly curved as shown. Furthermore, the cross-sectional shape of the recess 220 can be as follows: Figure 7EThe shape shown has multiple corners. Figures 7C to 7E In all the cases illustrated, these recesses 220 can be formed at the middle position in the thickness direction of the ceramic layer, or on the lower surface side, or multiple recesses can be formed, rather than on the upper surface side. In addition, when multiple recesses 220 are formed, their shapes can be different from each other.

[0139] The gas sensor element 100 of the above embodiment may further include a porous protective layer covering its front end and periphery. The porous protective layer is, for example, a porous ceramic material such as alumina. By including the porous protective layer, it is possible to prevent moisture in the gas being measured from entering the interior of the gas sensor element 100 and causing adverse effects on the gas sensor element 100.

[0140] Example

[0141] The embodiments of the present invention will now be described in detail. However, the present invention is not limited to these embodiments.

[0142] <Experiment 1>

[0143] Prepare to produce 5 images Figure 1 Six ceramic layers are stacked to form a gas sensor element with a heater. These gas sensor elements differ in the configuration of a pair of conductive sections that penetrate the first and second substrate layers and connect the resistive element of the heating element and the heater electrode; otherwise, they share a common configuration. Specifically, the cross-sectional shape of the inner wall surface of the through-hole in the second substrate layer that forms the conductive section is respectively set as follows: Figure 5 , Figure 6 , Figure 7A , Figure 7B and Figure 8 The cross-sectional shapes shown will be used as gas sensor elements in Examples 1-4 and Comparative Example 1, respectively. In the gas sensor element of Example 2, the cross-sectional shape of the inner wall surface of the through-hole in the second substrate layer is the same as that in the gas sensor element of Example 1; however, the inner wall surfaces of the through-holes in the first and second substrate layers are covered by insulating paste, which differs from the gas sensor element of Example 1. In the gas sensor element of Comparative Example 1, the through-hole in the second substrate layer is defined by a generally flat inner wall surface that extends substantially parallel to the entire thickness direction of the second substrate layer without defined recesses. In the gas sensor elements of Examples 1-4, when the thickness of the second substrate layer is set to 1, the depth of the recess determined using the method described in the above embodiments is 0.15.

[0144] The rear end side of the gas sensor elements, including a pair of conductive portions, of Examples 1-4 and Comparative Example 1 were immersed in water for 4 hours. Afterward, they were removed from the water and the water adhering to the surface was wiped away. Then, a voltage of 12V was applied to the heating element via the heater electrode for 30 seconds to confirm whether peeling had occurred between the second substrate layer, including the heating element and the heater insulating layer surrounding the heating element, and the third substrate layer. The results were evaluated in three stages, A to C.

[0145] A: We repeatedly applied voltage under the above conditions, but we did not confirm any stripping.

[0146] B: Stripping was confirmed during the second application of voltage.

[0147] C: Stripping was confirmed during the first application of voltage.

[0148] The results of Experiment 1 are shown in Table 1 below. As shown in Table 1, compared with Comparative Example 1, Examples 1-4 all showed significantly improved resistance to peeling. Furthermore, the results of Example 2 confirmed that even when the material in contact with the inner wall surface of the through-hole is a material other than conductive paste, the resistance to peeling is still improved. Experiment 1 above confirms the effectiveness of the present invention.

[0149] Table 1

[0150]

[0151] <Experiment 2>

[0152] Gas sensor elements were prepared by varying the depth of the recess relative to the thickness of the second substrate layer to 0.05, 0.10, 0.20, and 0.25 mm, respectively, based on the gas sensor element involved in Example 1. These gas sensor elements were then immersed in water under the same conditions as in Experiment 1. After wiping off the surface moisture, a voltage was applied under the same conditions as in Experiment 1, and the occurrence of peeling was confirmed in the same manner as in Experiment 1. The results were evaluated using the three stages described above (A to C).

[0153] The results of Experiment 2 are shown in Table 2 below. As shown in Table 2, the peel resistance was significantly improved in Examples 1, 6, and 7. In Example 5, perhaps because the depth of the recess was relatively shallow, the peel resistance was worse than in Examples 1, 6, and 7; however, it was improved compared to Comparative Example 1 and Reference Example 1. In Reference Example 1, peeling occurred. This was believed to be because the conductive paste did not penetrate sufficiently into the recess. Experiment 2 above confirms the effectiveness of the present invention.

[0154] Table 2

[0155]

Claims

1. A gas sensor element, wherein, have: Heating section; Multiple ceramic layers are stacked and configured to be heated by the heating element to form an internal space from which the gas to be measured is introduced from the external space; as well as The gas to be measured, introduced into the internal space, reaches the measuring electrode. The plurality of ceramic layers includes a first ceramic layer having: a first surface, a second surface located opposite to the first surface, and a through hole extending through the first ceramic layer along a thickness direction from the first surface toward the second surface, forming a through hole for electrically connecting the first surface side and the second surface side. The first ceramic layer is formed between the first surface and the second surface. The through hole is defined by a first inner wall surface extending along the thickness direction and a second inner wall surface that is continuous with the first inner wall surface and defines a recess that is recessed further inward than the first inner wall surface into the first ceramic layer. The second inner wall surface is formed at a position that is not continuous with the first surface and the second surface. When the thickness of the first ceramic layer is set to 1, the length of the first inner wall surface from the position closest to the central axis of the through hole to the innermost position of the recess is 0.05 or more and 0.20 or less.

2. The gas sensor element according to claim 1, wherein, When the thickness of the first ceramic layer is set to 1, the length of the first inner wall surface from the position closest to the central axis of the through hole to the innermost position of the recess is 0.10 or more and 0.20 or less.

3. The gas sensor element according to claim 1 or 2, wherein, The second inner wall surface is continuous over the entire circumference of the through hole, and the recess is defined by the second inner wall surface as being annular when viewed from the first surface side.

4. The gas sensor element according to claim 1 or 2, wherein, The second inner wall surface exists in at least one of a position biased towards the first surface and a position biased towards the second surface in the thickness direction.

5. The gas sensor element according to claim 1 or 2, wherein, There are multiple second inner wall surfaces along the thickness direction.

6. The gas sensor element according to claim 1 or 2, wherein, The gas sensor element also includes a conductive portion that is conductive and is configured to fill the interior of the through hole.

7. The gas sensor element according to claim 1 or 2, wherein, The heating element is disposed on the first side of the first ceramic layer. The through hole electrically connects the heating element and the element on the second side of the first ceramic layer.

8. The gas sensor element according to claim 1 or 2, wherein, The gas sensor element is configured to measure the concentration of nitrogen oxides in the gas being measured.

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