Sensor elements and gas sensors

Abstract

To provide a sensor element and a gas sensor which suppress variations in property of the gas sensor due to a hole in a reference lead part connected to an electrode.SOLUTION: A sensor element 100 comprises a detection electrode 106a and a reference electrode 104a, and a pair of lead parts respectively connected to the detection electrode and the reference electrode, and measures target components in measured gas using the detection electrode and the reference electrode. A reference lead part 104b connected to the reference electrode of the pair of lead parts includes: one or more types of noble metal particles 151 selected from a group consisting of Pt, Pd, Rh and Au; ceramic particles 153 with larger equivalent circle diameter than the noble metal particles; and holes G1, G2. When viewed in a section crossing a longer direction of the reference lead part, lead part thickness t<(maximum grain size M×3 of the ceramic particle)<lead part width W is satisfied.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a sensor element and a gas sensor suitably used for detecting the gas concentration of a specific gas contained in combustion gas or exhaust gas of, for example, combustors and internal combustion engines. Background Art

[0002] Gas sensors for detecting the concentration of a specific component (such as oxygen) contained in the exhaust gas of internal combustion engines are known. This type of gas sensor is internally provided with an elongated plate-shaped sensor element. A detection portion for detecting the specific component is provided at the distal end of the sensor element (see Patent Document 1). The detection portion is composed of a detection electrode, a reference electrode, and a solid electrolyte body, and a lead portion extends from each electrode toward the rear end side. Here, some reference lead portions connected to the reference electrode have pores formed inside, and adopt a structure that allows gas communication between the inside and outside of the element via the reference lead portion, thereby adjusting the pressure of the reference gas around the reference electrode. Prior Art Literature Patent Literature

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2022-032240 Summary of the Invention Problem to be Solved by the Invention

[0004] Incidentally, the reference lead portion is formed by screen-printing conductive paste or the like followed by firing. However, the printing thickness varies, and when the film thickness of the reference lead portion increases, the detection value (electromotive force) of the gas sensor decreases significantly, resulting in the problem of variations in the characteristics and quality of the gas sensor. This is considered to be because when the film thickness of the reference lead portion increases, the pores inside the lead portion become larger, and the gas to be measured easily escapes through the pores.

[0005] An object of the present invention is to provide a sensor element and a gas sensor that suppress fluctuations in characteristics of the gas sensor caused by voids in a reference lead portion connected to an electrode. [Means for Solving the Problem]

[0006] In order to solve the above problem, the sensor element of the present invention comprises: a detection electrode that comes into contact with a gas to be measured; a reference electrode that comes into contact with a reference gas; and a pair of lead portions respectively connected to the detection electrode and the reference electrode, wherein the sensor element measures a target component in the gas to be measured by the detection electrode and the reference electrode. Of the pair of lead portions, the reference lead portion connected to the reference electrode comprises one or more noble metal particles selected from the group consisting of Pt, Pd, Rh and Au, ceramic particles having an equivalent circle diameter larger than that of the noble metal particles, and voids, and when a cross section intersecting the longitudinal direction of the reference lead portion is viewed, the relationship of lead portion thickness t < (maximum particle diameter M of the ceramic particles × 3) < lead portion width W is satisfied.

[0007] When voids inside the reference lead portion become large, the gas to be measured easily escapes from the voids, which tends to cause changes in the characteristics of the gas sensor. The voids in the lead portion are considered to consist of internal voids and interface voids between the lead portion and other members respectively in contact with both surfaces of the lead portion. Among these, the area of the interface voids does not fluctuate greatly even when the film thickness t changes. Therefore, when t < M × 3, since the film thickness t is small, the number of internal voids is small, and interface voids account for most of all voids. Thus, even if the film thickness t changes, the total area of the voids does not fluctuate greatly, and fluctuations in the characteristics of the gas sensor can be suppressed. In contrast, when t ≧ M × 3, since the film thickness t is large, internal voids increase as the film thickness t increases, and the total area of the voids increases in accordance with the film thickness t. For this reason, the characteristics of the gas sensor also fluctuate in accordance with the film thickness t.

[0008] In the cross-section of the sensor element of the present invention, the pores consist of internal pores G1 inside the reference lead portion and interface pores G2 between other members respectively in contact with both surfaces of the reference lead portion, and the area of G1 may be 10% or less relative to the total area of G1 and G2. According to this sensor element, even if the film thickness t changes, the fluctuation of the total area of the pores G1 and G2 is further reduced, and the fluctuation of the characteristics of the gas sensor can be further suppressed.

[0009] The gas sensor of the present invention is characterized by comprising the sensor element described above and a metal shell that holds the sensor element. Effects of the Invention

[0010] According to the present invention, fluctuation in characteristics of a gas sensor caused by pores in a reference lead portion connected to an electrode can be suppressed. Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a cross-sectional view of a gas sensor cut along the axial direction. [Figure 2] FIG. 2 is an exploded perspective view schematically showing a detection element portion and a heater portion that constitute a sensor element. [Figure 3] FIG. 3 is a schematic view of a cross-section intersecting the longitudinal direction of a lead portion when t < M×3. [Figure 4] FIG. 4 is a schematic view of a cross-section intersecting the longitudinal direction of a lead portion when t ≧ M×3. [Figure 5] FIG. 5 is a diagram showing the relationship between the lead portion film thickness t and the characteristics (electromotive force) of a gas sensor. [Figure 6] FIG. 6 is a diagram showing a cross-sectional SEM image of a lead portion when t < M×3. [Figure 7] FIG. 7 is a diagram showing pores G1 and G2 extracted by image analysis of FIG. 6. [Figure 8] FIG. 8 is a diagram showing a cross-sectional SEM image of a lead portion when t ≧ M×3. [Figure 9] FIG. 9 is a diagram showing pores G1 and G2 extracted by image analysis of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described. First, the configuration of a gas sensor (oxygen sensor) 1 including a sensor element 100 according to the present embodiment will be described. FIG. 1 is a cross-sectional view of the gas sensor 1 cut along the axis L direction, and FIG. 2 is an exploded perspective view schematically showing a detection element portion 300 and a heater portion 200 that constitute the sensor element 100. In the present specification, the lower side of the gas sensor 1 shown in FIG. 1 is referred to as the "front end side", and the opposite side (the upper side in FIG. 1) is referred to as the "rear end side".

[0013] As shown in FIG. 1, the gas sensor 1 includes a sensor element 100 formed of a laminate of a detection element portion 300 and a heater portion 200, a metal holder 30 that accommodates and holds the sensor element 100 and the like therein, and a protector 24 attached to a front end portion of the metal holder 30. The sensor element 100 has an overall elongated plate shape, and is arranged such that its longitudinal direction is along the axis L direction. A porous protective layer 20 is formed on the front end side of the sensor element 100.

[0014] As shown in FIG. 2, the heater portion 200 has an overall elongated plate shape, and includes a first base body 101 and a second base body 103 mainly made of alumina, and a heating element 102 mainly made of platinum sandwiched between the first base body 101 and the second base body 103. The heating element 102 has a heating portion 102a located on the front end side, and a pair of heater lead portions 102b extending from the heating portion 102a along the longitudinal direction (axis L direction) of the first base body 101. An end of each heater lead portion 102b is electrically connected to a heater-side pad 120 via a conductor formed in a heater-side through hole 101a provided in the first base body 101.

[0015] Like the heater portion 200, the detection element portion 300 has an overall elongated plate shape, and includes an oxygen concentration detection cell 130 and an oxygen pump cell 140. The oxygen concentration detection cell 130 is composed of a first solid electrolyte body 105, and a first electrode 104 and a second electrode 106 formed on both surfaces of the first solid electrolyte body 105. The first electrode 104 is composed of a first electrode portion 104a, and a first lead portion 104b extending from the first electrode portion 104a along the longitudinal direction of the first solid electrolyte body 105 (the direction of the axis L). The second electrode 106 is composed of a second electrode portion 106a, and a second lead portion 106b extending from the second electrode portion 106a along the longitudinal direction of the first solid electrolyte body 105 (the direction of the axis L).

[0016] The end of the first lead portion 104b is electrically connected to the detection element-side pad 121 via conductors formed respectively in a first through hole 105a provided in the first solid electrolyte body 105, a second through hole 107a provided in an insulating layer 107 described later, a fourth through hole 109a provided in a second solid electrolyte body 109, and a sixth through hole 111a provided in a protective layer 111. The end of the second lead portion 106b is electrically connected to the detection element-side pad 121 via conductors formed respectively in a third through hole 107b provided in an insulating layer 107 described later, a fifth through hole 109b provided in the second solid electrolyte body 109, and a seventh through hole 111b provided in the protective layer 111.

[0017] The first electrode portion 104a and the second electrode portion 106a correspond to the "reference electrode" and the "detection electrode" recited in the claims, respectively, and the first lead portion 104b corresponds to the "reference lead portion" recited in the claims.

[0018] The oxygen pump cell 140 is composed of a second solid electrolyte body 109, and a third electrode 108 and a fourth electrode 110 formed on both surfaces of the second solid electrolyte body 109. The third electrode 108 is composed of a third electrode portion 108a, and a third lead portion 108b extending from the third electrode portion 108a along the longitudinal direction of the second solid electrolyte body 109 (the direction of the axis L). The fourth electrode 110 is composed of a fourth electrode portion 110a, and a fourth lead portion 110b extending from the fourth electrode portion 110a along the longitudinal direction of the second solid electrolyte body 109 (the direction of the axis L).

[0019] The end of the third lead portion 108b is electrically connected to the detection element side pad 121 via conductors formed in the fifth through-hole 109b provided in the second solid electrolyte 109 and the seventh through-hole 111b provided in the protective layer 111. The end of the fourth lead portion 110b is electrically connected to the detection element side pad 121 via a conductor formed in the eighth through-hole 111c provided in the protective layer 111. The second lead portion 106b and the third lead portion 108b are at the same potential.

[0020] The first solid electrolyte 105 and the second solid electrolyte 109 are composed of a partially stabilized zirconia sintered body obtained by adding yttria (Y2O3) or calcia (CaO) as a stabilizer to zirconia (ZrO2). The heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heater-side pad 120, and the detection element-side pad 121 can be formed from platinum group elements. Suitable platinum group elements for forming these include Pt, Rh, and Pd. These platinum group elements may be used individually or in combination of two or more.

[0021] From the viewpoint of heat resistance and oxidation resistance, the above-mentioned heating element 102, etc., is preferably formed mainly of Pt. Furthermore, it is preferable that the above-mentioned heating element 102, etc., contains a ceramic component in addition to the main platinum group element. From the viewpoint of adhesion, it is preferable that this ceramic component has the same composition as the main material of the layer to which it is laminated.

[0022] An insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130 described above. The insulating layer 107 consists of an insulating portion 114 and a diffusion resistance portion 115. In the insulating portion 114 of the insulating layer 107, a hollow measurement chamber 107c is formed at positions corresponding to the second electrode portion 106a and the third electrode portion 108a. This measurement chamber 107c is in communication with the outside in the width direction of the insulating layer 107, and a diffusion resistance portion 115 is arranged in the communication portion to realize gas diffusion between the outside and the measurement chamber 107c under predetermined rate-limiting conditions. The insulating part 114 is not limited to any ceramic sintered body having insulating properties, and is made of, for example, an oxide ceramic such as alumina or mullite. The diffusion resistance section 115 is a porous material made of alumina, and this porous diffusion resistance section 115 adjusts the rate at which the detected gas flows into the measurement chamber 107c.

[0023] Furthermore, a protective layer 111 is formed on the surface of the second solid electrolyte 109, sandwiching the fourth electrode 110. This protective layer 111 consists of a porous electrode protection portion 113a that sandwiches the fourth electrode portion 110a to protect it from poisoning, and a reinforcing portion 112 that sandwiches the fourth lead portion 110b to protect the second solid electrolyte 109. In this embodiment, the sensor element 100 is an oxygen sensor element that linearly detects the oxygen concentration in the gas to be measured according to the current flowing through the oxygen pump cell 140, by adjusting the direction and magnitude of the current flowing between the electrodes of the oxygen pump cell 140 so that the voltage (electromotive force) generated between the electrodes of the oxygen concentration detection cell 130 becomes a predetermined value (for example, 450 mV).

[0024] Here, when viewing a cross-section of the sensor element 100 perpendicular to the axis L, the outer edge consisting of the protective layer 111 and the first substrate 101 forms the longer side, and the two sides along the stacking direction form the shorter sides, resulting in a rectangular cross-section.

[0025] Returning to Figure 1, the main fitting 30 is made of SUS430 and has a male threaded portion 31 for attaching the gas sensor 1 to the exhaust pipe and a hexagonal portion 32 for applying the attachment tool during installation. The main fitting 30 is also provided with a fitting-side stepped portion 33 that protrudes radially inward, and this fitting-side stepped portion 33 supports a metal holder 34 for holding the sensor element 100. Inside this metal holder 34, a ceramic holder 35 and a talc 36 are arranged in order from the tip side. This talc 36 consists of a first talc 37 positioned inside the metal holder 34 and a second talc 38 positioned at the rear end of the metal holder 34. The sensor element 100 is fixed to the metal holder 34 by the compression and filling of the first talc 37 inside the metal holder 34. Furthermore, the sealing between the outer surface of the sensor element 100 and the inner surface of the main body fitting 30 is ensured by the compression and filling of the second talc 38 inside the main body fitting 30.

[0026] An alumina sleeve 39 is positioned at the rear end of the second talc stone 38. This sleeve 39 is formed in a multi-stage cylindrical shape, with an axial hole 39a provided along the axis L, and the sensor element 100 is inserted inside the sleeve 39, including the axial hole 39a. A crimping portion 30a at the rear end of the main fitting 30 is bent inward, and this crimping portion 30a presses the sleeve 39 against the front end of the main fitting 30 via a stainless steel ring member 40.

[0027] Furthermore, a metal protector 24 is attached to the outer circumference of the tip side of the main fitting 30 by welding. The protector 24 has a double structure, with a bottomed cylindrical outer protector 41 having a uniform outer diameter on the outside and a bottomed cylindrical inner protector 42 having an outer diameter at the rear end 42a that is larger than the outer diameter at the tip 42b on the inside. This protector 24 covers the tip of the sensor element 100 that protrudes from the tip of the main fitting 30 and has a plurality of gas intake holes 24a.

[0028] The distal end side of an outer cylinder 25 made of SUS430 is inserted into the rear end side of the main metal fitting 30. The outer cylinder 25 includes a distal end portion 25a whose diameter is expanded on the distal end side, and the distal end portion 25a is fixed to the main metal fitting 30 by laser welding or the like. A separator 50 is arranged inside the rear end side of the outer cylinder 25, and a holding member 51 is interposed in a gap formed between the separator 50 and the outer cylinder 25. The holding member 51 is fixed between the crimped outer cylinder 25 and the separator 50 while engaging with a protruding portion 50a that bulges outward from the peripheral surface of the separator 50.

[0029] Further, the separator 50 is provided with insertion holes 50b for inserting various lead wires 11, 12, 13 for the detection element portion 300 and the heater portion 200, in a form penetrating from the distal end side to the rear end side. For convenience of explanation, only three lead wires 11, 12, 13 are shown in FIG. 1, and illustration of lead wires other than these is omitted. A connection terminal 16 that connects the lead wires 11 and the like, the detection element side pad 121 of the detection element portion 300, and the heater side pad 120 of the heater portion 200 is accommodated in the insertion hole 50b. Each of the lead wires 11 and the like is configured to be connectable to an unillustrated connector outside, and input and output of electrical signals are performed between an external device such as an ECU and each of the lead wires 11 and the like via such a connector.

[0030] Further, a substantially cylindrical rubber cap 52 for closing the opening 25b on the rear end side of the outer cylinder 25 is arranged on the rear end side of the separator 50. The rubber cap 52 is fixed to the outer cylinder 25 by crimping the outer cylinder 25 radially inward while being accommodated in the rear end of the outer cylinder 25. The rubber cap 52 is also provided with insertion holes 52a for respectively inserting the lead wires 11 and the like, in a form penetrating from the distal end side to the rear end side.

[0031] Next, the first lead portion 104b, which is a characteristic part of the present invention, will be described. FIG. 3 is a schematic cross-sectional view intersecting the longitudinal direction of the first lead portion 104b when t<M×3. As shown in FIG. 3, the first lead portion 104b comprises one or more noble metal particles 151 selected from the group consisting of Pt, Pd, Rh and Au, ceramic particles 153 having a circle-equivalent diameter larger than that of said noble metal particles, and voids G1 and G2, and is formed of a gas-permeable porous body.

[0032] The first lead portion 104b faces communication holes provided in the sensor element 100 (the first through hole 105a, the second through hole 107a, the fourth through hole 109a and the sixth through hole 111a) and communicates with the outside. A detection element-side pad 121 electrically connected to the sixth through hole 111a is also formed of a gas-permeable porous body. External reference atmosphere is supplied to the first electrode portion 104a, which serves as a reference electrode, via the detection element-side pad 121, the communication holes, and the first lead portion 104b. It should be noted that the particle diameters of the noble metal particles 151 and the ceramic particles 153 are obtained by performing composition analysis on the noble metal particles 151 and the ceramic particles 153 in a cross-sectional view intersecting the longitudinal direction of the first lead portion 104b (such as an SEM image, see FIG. 3), and respectively obtaining the circle-equivalent diameters of the image matching the contrast of each particle.

[0033] Here, as shown in FIG. 3, the relationship of lead portion film thickness t < (maximum particle diameter M of ceramic particles 153 × 3) < lead portion width W is satisfied. The voids of the first lead portion 104b consist of internal voids G1 and interface voids G2 between other members (the second base body 103 and the first solid electrolyte body 105) respectively in contact with both surfaces of the first lead portion 104b. Among these, the area of the interface voids G2 does not vary greatly even if the film thickness t changes. Therefore, if t < M × 3, the film thickness t is small, so the number of internal voids G1 is small (G1 may even be zero when t is small), and among the voids G1 and G2, interface voids G2 account for the majority. Thus, even if the film thickness t changes, the total area of the voids G1 and G2 does not vary greatly, and the fluctuation of the detection value (electromotive force) of the gas sensor which causes fluctuation of the characteristics of the gas sensor can be suppressed.

[0034] In contrast, as shown in Fig. 4, when t≧M×3, the film thickness t is large, so as the film thickness t increases, the number of internal voids G1 increases, and the total area of voids G1 and G2 increases in accordance with the film thickness t. For this reason, the detection value (electromotive force) of the gas sensor fluctuates according to the film thickness t, and the characteristics of the gas sensor also fluctuate.

[0035] The reason for defining M×3<W is that if W is too narrow compared to t, the proportion of interface voids G2 among voids G1 and G2 greatly decreases, and even when t<M×3, the total area of voids G1 and G2 also fluctuates along with variations in the film thickness t.

[0036] When the area of G1 is 10% or less with respect to the total area of G1 and G2, the fluctuation in the total area of voids G1 and G2 becomes even smaller even if the film thickness t changes, and fluctuation in the characteristics of the gas sensor can be further suppressed.

[0037] The method for measuring the film thickness t of the first lead portion 104b is performed based on a cross-sectional SEM image including the first lead portion 104b as shown in Fig. 6. Note that Fig. 6 is a cross-sectional SEM image of an example described later. First, a cross-sectional SEM image is subjected to image analysis and binarization, and voids G1 and G2 are extracted by regarding a predetermined shading as void portions (binarization software: ImageJ). The extraction result is shown in Fig. 7. Voids G1 and G2 are the darkest parts in the cross-sectional SEM image, and the noble metal particles 151 constituting the first lead portion 104b are the brightest parts. Further, the ceramic particles 153 constituting the first lead portion 104b have intermediate brightness. Further, the film thickness t is the average value of the widths at three locations of the first lead portion 104b.

[0038] Furthermore, since void G2 is an "interface void between the first lead portion 104b and other members (second substrate 103 and first solid electrolyte 105) that are in contact with both sides (both ends in the thickness direction) of the first lead portion 104b, the voids in contact with the outside of the first lead portion 104b are counted as G2, and the others are counted as void G1 (Figure 7). Each void is counted using the Analyze Particle command of the binarization software, and the area of ​​each void is then calculated. This allows us to calculate the total area of ​​G1 and the total area of ​​G2.

[0039] Next, a parallel line BL is drawn from the outermost end of the void G2 that connects to the precious metal particle 151 and is located in the thickness direction of the first lead portion 104b (vertical direction in Figure 6), in the plane direction of the first lead portion 104b (left-right direction in Figure 6). The parallel line BL is drawn on the upper and lower sides of the first lead portion 104b, respectively. Then, the region of the cross-sectional SEM image enclosed by the two parallel lines BL is considered as the first lead portion 104b, and the distance between the two parallel lines BL in the thickness direction is calculated as the film thickness t. Furthermore, any voids that do not connect to the precious metal particles 151 (i.e., those further from the precious metal particles 151 than the parallel line BL) are considered to be internal voids (spaces) in other layers adjacent to the first lead portion 104b, and are therefore excluded. Furthermore, if another precious metal particle 151 is located furthest out in the thickness direction from the void G2 connected to that precious metal particle 151, the position of that precious metal particle 151 is defined as the parallel line BL.

[0040] The method for measuring the maximum particle size M of the ceramic particle 153 is to take the above-mentioned cross-sectional SEM image and, within the region of the first lead portion 104b enclosed by two parallel lines BL, take the maximum equivalent circular diameter of the closed portion where the outer edge can be identified among the bright areas considered to be ceramic particles 153. For example, in the cross-section of Figure 6, among several ceramic particles 153 whose outer edges can be identified, the equivalent circular diameter of ceramic particle 153M was taken as the maximum particle size M.

[0041] The present invention is not limited to the above-described embodiment. The sensor element only needs to have a pair of electrodes and a pair of leads, and can be applied to the oxygen sensor (oxygen sensor element) of the present embodiment. However, it is not limited to these applications, and it goes without saying that the present invention covers various modifications and equivalents included in the spirit and scope of the present invention. For example, the present invention may be applied to a full-range oxygen sensor having an oxygen pump cell, a NOx sensor (NOx sensor element) that detects NOx concentration in a gas to be measured, an HC sensor (HC sensor element) that detects HC concentration, and the like. Further, the sensor element may be of a cylindrical type, or may be a binary sensor or a linear sensor. [Examples]

[0042] <Evaluation of Characteristics (Electromotive Force) of Gas Sensor> A plate-shaped sensor element (oxygen sensor element) 100 shown in FIG. 1 and FIG. 2 was manufactured. Here, as the first lead portion 104b, a paste containing noble metal particles made of Pt and alumina particles 153 having a larger equivalent circle diameter than the noble metal particles was screen-printed at a predetermined position of the sensor element, and then the whole was fired to form the first lead portion 104b. A plurality of sensor element samples were produced by changing the printing thickness.

[0043] Next, the sensor element 100 was assembled into the gas sensor 1, the gas sensor was heated to a measurement temperature, and the characteristics (electromotive force) of the gas sensor were evaluated in an atmosphere to be measured. The smaller the fluctuation of the electromotive force even when the thickness of the first lead portion 104b fluctuates, the better the performance is. The obtained results are shown in FIG. 5. FIG. 5 shows the relationship between the lead portion film thickness t and the characteristics (electromotive force) of the gas sensor. As shown in FIG. 5, it was found that when t < M×3, the change in the detection value (electromotive force) of the gas sensor is small with respect to the change in the lead portion film thickness t. On the other hand, when t ≧ M×3, the change in the detection value (electromotive force) of the gas sensor increased with respect to the change in the lead portion film thickness t.

[0044] FIG. 6 and FIG. 8 are cross-sectional SEM images of the first lead portion 104b when t < M×3 and t ≧ M×3, respectively. Further, FIG. 7 and FIG. 9 show voids G1 and G2 extracted by image analysis of FIG. 6 and FIG. 8, respectively. From the cross-sectional image shown in FIG. 6, when the area of G1 was calculated with respect to the total area of G1 and G2 by image analysis, it was 0.6%. Further, in another cross-sectional image (not shown) where t < M×3, the area was 9.3%. On the other hand, from the cross-sectional image shown in FIG. 8, when the area of G1 was calculated with respect to the total area of G1 and G2 by image analysis, it was 42.7%. Further, in another cross-sectional image (not shown) where t ≧ M×3, the area was 22.8%. From this, it can be seen that the area of G1 is preferably 10% or less relative to the total area of G1 and G2. [Description of Reference Numerals]

[0045] 1 gas sensor 30 metallic holder 100 sensor element 104a reference electrode 106a detection electrode 104b reference lead portion 151 noble metal particles 153 ceramic particles G1, G2 voids

Claims

1. A detection electrode that comes into contact with the gas to be measured and a reference electrode that comes into contact with the reference gas, A sensor element comprising a pair of lead portions connected to the detection electrode and the reference electrode, respectively, wherein the detection electrode and the reference electrode measure a target component in the gas to be measured, Of the pair of lead portions, the reference lead portion connected to the reference electrode is composed of one or more precious metal particles selected from the group Pt, Pd, Rh, and Au, ceramic particles having a larger equivalent diameter than the precious metal particles, and pores. A sensor element characterized in that, when viewing a cross-section intersecting the longitudinal direction of the reference lead portion, the relationship t < (maximum particle size M × 3 of the ceramic particles) < width W of the lead portion is satisfied.

2. In the cross-section, the void consists of an internal void G1 of the reference lead portion and an interface void G2 between the reference lead portion and other members that are in contact with both sides of the reference lead portion. The sensor element according to claim 1, characterized in that the area of ​​G1 is 10% or less of the total area of ​​G2.

3. A sensor element according to claim 1 or 2, A main metal fitting that holds the sensor element, A gas sensor characterized by having the following features.

Images