Sensor element and gas sensor

Abstract

The invention provides a sensor element and a gas sensor, which can suppress the reduction of the detection precision of the concentration of a specific gas. A sensor element (101) is provided with: an element main body (102) having a solid electrolyte layer having oxygen ion conductivity; a measurement electrode (44) disposed inside the element main body (102); and a conduction section (74) in which the inner lead section (77), the side lead section (78), and the connector electrode (75a) are connected in this order to the measurement electrode (44). The side surface lead portion (78) covers the left end of the fourth portion (77d) of the inner side lead portion (77), and satisfies Rp / Dc < = 145% / mm, where Rp [%] is the porosity and Dc [mm] is the thickness.

Description

Technical Field The present invention relates to a sensor element and a gas sensor. Background Art In the past, a gas sensor having a sensor element is known, which is used to detect the concentration of a specific gas such as NOx in a measured gas such as the exhaust gas of an internal combustion engine (see, for example, Patent Document 1). The sensor element of Patent Document 1 comprises: an element body, an inner electrode, a terminal portion, and a lead portion. The element body has an oxygen ion conductive solid electrolyte layer, is in a columnar shape extending along the length direction, and has a front end and a rear end as two ends along the length direction and a side surface as a surface along the length direction. The front end side of the element body is exposed to the measured gas. The inner electrode is arranged inside the element body. The terminal portion is arranged on the rear end side of the side of the element body. The lead portion is configured to connect the inner electrode and the terminal portion, and has an inner portion arranged inside the element body, and a side conductive portion exposed from the element body on the side. Prior art literature Patent Literature Patent Document 1: Japanese Patent No. 4628920 Summary of the invention In this sensor element, some gas outside the sensor element (element body) sometimes intrudes into the interior of the element body from the end of the side conductive portion of the inner portion of the lead portion or the gap between it and the element body, moves toward the inner electrode along the inner portion or the gap between it and the element body, and reaches the inner electrode. When the gas reaches the inner electrode, the detection accuracy of the concentration of the specific gas may be reduced. The main object of the sensor element and the gas sensor of the present invention is to suppress a decrease in the detection accuracy of the concentration of a specific gas. The sensor element and the gas sensor of the present invention adopt the following means to achieve the above-mentioned main object.

[0001] The gist of the sensor element of the present invention is that It is a sensor element used to detect the concentration of a specific gas in the measured gas. The sensor element comprises: an element body having an oxygen ion conductive solid electrolyte layer and in a columnar shape extending in a longitudinal direction, having a front end and a rear end as both ends along the longitudinal direction and a side surface as a surface along the longitudinal direction, wherein the front end side is exposed to the measured gas; an inner electrode disposed inside the element body; and Conductive part, The conductive portion includes: an inner conductive portion, which is arranged inside the element body and is conductively connected to the inner electrode; and an outer conductive portion, which has a connector electrode arranged on the rear end side of the side surface, and has a portion arranged on the side surface and / or a portion exposed to the outside of the sensor element on the side surface, and is conductively connected to the inner conductive portion. Regarding the covering portion of the outer conductive portion that covers the inner conductive portion, when its porosity is Rp [%] and its thickness is Dc [mm], Rp / Dc ≤ 145% / mm is satisfied. In the sensor element of the present invention, when the porosity of the covered portion of the outer conductive portion covering the inner conductive portion is set to Rp [%] and the thickness is set to Dc [mm], Rp / Dc ≤ 145% / mm is satisfied. As a result, it is possible to suppress certain gases outside the sensor element (element body) from passing through the portion of the outer conductive portion covering the inner conductive portion, thereby suppressing these gases from invading the inside of the element body from the inner conductive portion or the gap between it and the element body, and suppressing these gases from reaching the inner electrode. As a result, it is possible to suppress the reduction in the detection accuracy of the concentration of a specific gas. The inventors of the present invention have confirmed the above situation through experiments, analysis, etc.

[0002] In the sensor element of the present invention (the sensor element described in [1] above), the covering portion may satisfy Rp / Dc ≤ 120% / mm. This can further suppress some gas outside the sensor element (element body) from passing through the portion of the outer conductive portion that covers the inner conductive portion.

[0003] In the sensor element of the present invention (the sensor element described in [1] or [2] above), the coating portion may satisfy Rp / Dc ≥ 1.5% / mm. This can improve the adhesion between the coating portion and the element body. The inventors of the present invention have confirmed the above through experiments, analysis, etc.

[0004] In the sensor element of the present invention (the sensor element described in [3] above), the coating portion may satisfy Rp / Dc ≥ 4.5% / mm. This can further improve the adhesion between the coating portion and the element body.

[0005] In the sensor element of the present invention (the sensor element according to any one of [1] to [4] above), the porosity Rp may be 0.01% or more and 9.0% or less.

[0006] In the sensor element of the present invention (the sensor element according to any one of [1] to [5] above), the thickness Dc may be greater than or equal to 0.001 mm and less than or equal to 0.080 mm.

[0007] In the sensor element of the present invention (the sensor element described in any one of [1] to [6] above), the inner electrode may be a measurement electrode for detecting the concentration of the specific gas.

[0008] In the sensor element of the present invention (the sensor element described in any one of [1] to [7] above), the element body can be: a stacked body obtained by stacking a plurality of layers including the solid electrolyte layer along a stacking direction orthogonal to the length direction, in which the stacked body has, as the side surface, a first surface and a second surface as two end surfaces in the stacking direction, and a third surface and a fourth surface as two end surfaces in a direction orthogonal to the length direction and the stacking direction, the inner conductive portion has: an inner lead portion led out to the third surface or the fourth surface, and the covered portion is: a side lead portion arranged on the third surface or the fourth surface and covering the inner lead portion.

[0009] In the sensor element of the present invention (the sensor element described in any one of [1] to [7] above), the element body may be: a stacked body obtained by stacking a plurality of layers including the solid electrolyte layer along a stacking direction orthogonal to the length direction, in which the stacked body has, as the side surface, a first surface and a second surface as two end surfaces in the stacking direction, the element body has: a through hole that penetrates one or more of the plurality of layers along the stacking direction, and the through hole includes: an opening portion that is open to the first surface or the second surface on the rear end side of the side surface, the inner conductive portion has: a through hole conductor arranged in the through hole, and the covered portion is the connector electrode and covers the through hole conductor.

[0010] In the sensor element of the present invention (the sensor element described in any one of [1], [2], [5] to [7] above), the element body may be a stacked body obtained by stacking a plurality of layers including the solid electrolyte layer in a stacking direction orthogonal to the longitudinal direction, wherein the stacked body has, as the side surface, a first surface and a second surface as two end surfaces in the stacking direction, the element body has a through hole that penetrates one or more of the plurality of layers in the stacking direction, and the through hole includes an opening portion that is open to the first surface or the second surface on the rear end side of the side surface, and the covering portion includes a portion of the through-hole conductor that is connected to the connector electrode and is exposed to the outside, including a portion that is arranged in the through-hole and exposed to the outside in the opening portion. In this case, the covering portion may be a part of the through-hole conductor or the entirety.

[0011] The sensor element of the present invention (the sensor element described in any one of [1] to

[10] above) can be used in a gas sensor, which comprises: the sensor element; a shell, which is in the shape of a tube extending along the length direction of the sensor element, and has a second front end and a second rear end as two ends along the length direction, and the sensor element is arranged inside; and a closing component, which closes the second rear end side of the shell.

[0012] The gist of the gas sensor of the present invention is that it comprises: a sensor element as described in any one of [1] to

[10] above; a shell, which is in the shape of a tube extending along the length direction of the sensor element, and has a second front end and a second rear end as two ends along the length direction, and the sensor element is arranged inside; and a closing component, which closes the second rear end side of the shell. The gas sensor of the present invention has the above-mentioned sensor element, and therefore can exert the same effects as those exerted by the above-mentioned sensor element, such as being able to suppress certain gases outside the sensor element (element body) from reaching the inner electrode and suppressing the reduction in the detection accuracy of the concentration of a specific gas, etc. Here, as certain gases outside the sensor element, for example, there can be cited gases generated by a sealing member (for example, volatile organic gases generated by a rubber stopper as a sealing member). BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a longitudinal cross-sectional view of the gas sensor 100 . Figure 2 It is a cross-sectional schematic diagram schematically showing an example of the structure of the sensor element 101 . Figure 3 It is a block diagram showing the electrical connection relationship between the control device 95 and each unit. Figure 4 It is a perspective view of the vicinity of the rear end portion of the element body 102 . Figure 5 It is a partial cross-sectional view showing an enlarged view of the periphery of the conductive portion 74 corresponding to the measuring electrode 44 . Figure 6 2 is a partial cross-sectional view of a sensor element 201 according to a modified example. Figure 7 2 is a partial cross-sectional view of a sensor element 301 according to a modified example. Figure 8 4 is a partial cross-sectional view of a sensor element 401 according to a modified example. Fig. 9 2 is a partial cross-sectional view of a sensor element 501 according to a modified example. Fig.10 2 is a schematic cross-sectional view of a sensor element 601 according to a modified example. Fig.11 It is an explanatory diagram showing the specifications of each experimental example. Fig.12 It is an explanatory diagram of a method for checking whether or not there is separation between the side lead portion 78 and the element body 102 . Fig.13 It is an explanatory diagram of a method for checking whether or not there is separation between the side lead portion 78 and the element body 102 . Explanation of symbols 1... First substrate layer, 2... Second substrate layer, 3... Third substrate layer, 4... First solid electrolyte layer, 5... Isolation layer, 6... Second solid electrolyte layer, 7... Adhesive layer, 10... Gas inlet, 11... First diffusion rate control section, 12... Buffer space, 13... Second diffusion rate control section, 20... First internal cavity, 21... Main pump unit, 22... Inner pump electrode, 22a, 51a... Top electrode portion, 22b, 51b... Bottom electrode portion, 23... Outer pump electrode, 24... Variable power supply, 30... Third diffusion rate control section, 40... Second internal cavity, 41... Measurement pump unit, 42... Reference electrode, 43... Reference gas introduction space, 44... Measurement electrode, 45... Fourth diffusion rate control section, 46... Variable power supply, 48... Reference gas introduction layer, 49... Reference gas introduction portion, 49a... Inlet portion, 50... Auxiliary pump unit, 51... Auxiliary pump electrode, 52... Variable power supply, 60... Fourth diffusion rate control section, 61... Third internal cavity, 70... Heater section, 71a... Heater, 71b... Heater insulation layer, 71c... Pressure release hole, 72... Heater power supply, 74... Conductive portion, 75, 75a - 75h, 575a... Connector electrode, 76... Lead portion, 77, 477... Inner lead portion, 77a - 77d... First - fourth portions, 78, 278, 378... Side lead portion, 79... Lead insulation layer, 80... Main pump control oxygen partial pressure detection sensor unit, 81... Auxiliary pump control oxygen partial pressure detection sensor unit, 82... Measurement pump control oxygen partial pressure detection sensor unit, 83... Sensor unit, 95... Control device, 96... Control section, 97... CPU, 98... Storage section, 100... Gas sensor, 101, 201, 301, 401, 501, 601... Sensor element, 102, 402... Element body, 102a... First face, 102b... Second face, 102c... Third face, 102d... Fourth face, 102e... Fifth face, 102f... Sixth face, 130... Protective cover, 131... Inner protective cover, 132... Outer protective cover, 133... Sensor element chamber, 140... Sensor assembly, 141... Element enclosure, 142... Main body metal part, 143... Inner cylinder, 143a, 143b... Reduced diameter portion, 144a - 144c... Ceramic support, 145a, 145b... Compressed powder body, 146... Metal ring, 147... Bolt, 148... Outer cylinder, 149... Space, 150... Connector, 155... Lead, 157... Rubber plug, 190... Pipe, 191... Fixing part, 278a, 378a... First side lead portion, 278b, 378b... Second side lead portion, 402h... Through hole, 478, 578... Through hole conductor, 479... Insulation layer, 575h... Hole. Detailed implementation mode Next, the embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 1 is a longitudinal sectional view of a gas sensor 100 according to one embodiment of the present invention. Figure 2 1 is a schematic cross-sectional view schematically showing an example of the configuration of a sensor element 101 included in the gas sensor 100 . Figure 3 It is a block diagram showing the electrical connection relationship between the control device 95, each unit of the sensor element 101, and the heater 71a. Figure 4 It is a perspective view of the vicinity of the rear end portion of the element body 102 of the sensor element 101 . Figure 5 FIG. 1 is a partial cross-sectional view of the periphery of the measuring electrode 44 and the corresponding conductive portion 74 of the sensor element 101. The sensor element 101 has a long rectangular parallelepiped element body 102. The length direction ( Figure 2 The left-right direction in the figure) is set as the front-to-back direction, and the thickness direction of the element body 102 ( Figure 2 The vertical direction in FIG. 1 is set as the vertical direction, and the width direction of the element body 102 (the direction perpendicular to the front-rear direction and the vertical direction) is set as the left-right direction. The element body 102 is a rectangular parallelepiped. Figure 2 , Figure 4 , Figure 5 As shown, the outer surface of the solid electrolyte layer serving as the element body 102 has six surfaces: a first surface 102a (upper surface), a second surface 102b (lower surface), a third surface 102c (left side surface), a fourth surface 102d (right side surface), a fifth surface 102e (front end surface), and a sixth surface 102f (rear end surface). like Figure 1 As shown in the figure, the gas sensor 100 comprises: a sensor element 101 having an element body 102; a protective cover 130 which protects the front end side of the element body 102; and a sensor assembly 140 having a connector 150 which is in electrical communication with the sensor element 101. As shown in the figure, the gas sensor 100 is mounted on a pipe 190 such as an exhaust pipe of an internal combustion engine (diesel engine, gasoline engine, etc.) of a vehicle, and is used to: use the exhaust gas of the internal combustion engine as the measured gas to measure NOx, O 2 In the present embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration. The protective cover 130 includes an inner protective cover 131 having a bottomed cylindrical shape, which covers the front end of the element body 102, and an outer protective cover 132 having a bottomed cylindrical shape, which covers the inner protective cover 131. The inner protective cover 131 and the outer protective cover 132 are formed with a plurality of holes for allowing the measured gas to flow in the protective cover 130. The sensor element chamber 133 is formed as a space surrounded by the inner protective cover 131, and the front end of the element body 102 is arranged in the sensor element chamber 133. The sensor assembly 140 comprises: an element enclosure 141, which seals and fixes the sensor element 101; bolts 147 and an outer cylinder 148, which are mounted on the element enclosure 141; and a connector 150, which contacts the connector electrodes 75 formed on the surface (upper and lower surfaces) of the rear end of the element body 102 of the sensor element 101 and is electrically connected to these electrodes. The element enclosure 141 includes: a cylindrical main metal member 142; a cylindrical inner tube 143, which is welded and fixed coaxially with the main metal member 142; and ceramic supports 144a to 144c, pressed powder bodies 145a and 145b, and a metal ring 146, which are sealed in through holes on the inner sides of the main metal member 142 and the inner tube 143. The sensor element 101 is located on the central axis of the element enclosure 141 and penetrates the element enclosure 141 in the front-rear direction. The inner tube 143 is formed with: a reduced diameter portion 143a, which is used to press the pressed powder body 145b in the central axis direction of the inner tube 143; and a reduced diameter portion 143b, which is used to press the ceramic supports 144a to 144c and the pressed powder bodies 145a and 145b forward by means of the metal ring 146. The pressed powder bodies 145a and 145b are compressed between the main metal part 142 and the inner tube 143 and the sensor element 101 by the pressing force from the reduced diameter parts 143a and 143b, thereby sealing the space between the sensor element chamber 133 in the protective cover 130 and the space 149 in the outer tube 148 and fixing the sensor element 101. The bolt 147 is fixed coaxially with the main metal fitting 142, and an external thread portion is formed on the outer peripheral surface of the bolt 147. The external thread portion of the bolt 147 is inserted into the fixing member 191, which is welded to the pipe 190 and has an internal thread portion on the inner peripheral surface. Thus, the gas sensor 100 is fixed to the pipe 190 in a state where the front end portion of the element body 102 of the sensor element 101 in the gas sensor 100 and a portion of the protective cover 130 protrude into the pipe 190. The outer cylinder 148 covers the inner cylinder 143, the sensor element 101 and the connector 150, and a plurality of lead wires 155 connected to the connector 150 are led out from the rear end to the outside. The lead wires 155 are connected to the electrodes (described later) of the sensor element 101 by means of the connector 150. At the rear end side of the outer cylinder 148, the gap between the outer cylinder 148 and the lead wires 155 is closed by a rubber plug 157. The outer cylinder 148 is formed with rivets 148a and 148b for limiting the relative movement of the rubber plug 157 in the front-rear direction relative to the outer cylinder 148. The space 149 in the outer cylinder 148 is filled with a reference gas. The rear end of the element body 102 of the sensor element 101 is arranged in the space 149. like Figure 2 As shown in FIG. 1 , the sensor element 101 includes an element body 102, units 21, 41, 50, 80 to 83, and a heater unit 70. The element body 102 is composed of zirconium dioxide (ZrO 2 ) and the like. The first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6 are stacked to obtain a stacked body. In addition, the solid electrolyte forming these 6 layers is a dense gas-tight solid electrolyte. The element body 102 is manufactured in the following manner: for example, the ceramic green sheets corresponding to each layer are subjected to predetermined processing and circuit pattern printing, and then they are stacked and then fired to achieve integration. On the front end side of the element body 102 and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, there are adjacently formed in a sequentially connected manner: a gas inlet 10, a first diffusion rate control section 11, a buffer space 12, a second diffusion rate control section 13, a first internal cavity (oxygen concentration adjustment chamber) 20, a third diffusion rate control section 30, a second internal cavity (oxygen concentration adjustment chamber) 40, a fourth diffusion rate control section 60 and a third internal cavity (measurement chamber) 61. The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40 and the third internal cavity 61 are spaces inside the sensor element 101 that are arranged by hollowing out the isolation layer 5, wherein the upper part of the space is separated by the lower surface of the second solid electrolyte layer 6, the lower part of the space is separated by the upper surface of the first solid electrolyte layer 4, and the side of the space is separated by the side of the isolation layer 5. The first diffusion rate control section 11, the second diffusion rate control section 13, and the third diffusion rate control section 30 are all provided with two horizontally long slits (the length direction of the opening is in the direction perpendicular to the drawing). In addition, the fourth diffusion rate control section 60 is provided with a horizontally long slit (the length direction of the opening is in the direction perpendicular to the drawing) formed as a gap between the lower surface of the second solid electrolyte layer 6. In addition, the portion from the gas inlet 10 to the third internal cavity 61 is also referred to as the measured gas flow section. The element body 102 is provided with a reference gas introduction part 49 for allowing a reference gas to flow from the outside of the element body 102 to the reference electrode 42 when measuring the NOx concentration. The reference gas introduction part 49 has a reference gas introduction space 43 and a reference gas introduction layer 48. The reference gas introduction space 43 is a space provided in a manner extending from the sixth surface 102f (rear end surface) of the element body 102 toward the fifth surface 102e (front end surface) side. The reference gas introduction space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the isolation layer 5, and is provided at a position where the side portion is separated by the side surface of the first solid electrolyte layer 4. The reference gas introduction space 43 is open at the rear end surface of the element body 102, and the opening functions as an inlet 49a of the reference gas introduction part 49. The reference gas is introduced into the reference gas introduction space 43 from the inlet 49a. The reference gas introduction part 49 applies a predetermined diffusion resistance to the reference gas introduced from the inlet 49a, and introduces the reference gas to the reference electrode 42. In this embodiment, the reference gas is set to atmospheric air. The reference gas introduction layer 48 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is a porous body composed of ceramics such as alumina. A portion of the upper surface of the reference gas introduction layer 48 is exposed in the reference gas introduction space 43. The reference gas introduction layer 48 is formed to cover the reference electrode 42. The reference gas introduction layer 48 allows the reference gas to flow from the reference gas introduction space 43 to the reference electrode 42. The reference electrode 42 is an electrode formed by being sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around it. In addition, as described later, the reference electrode 42 can be 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 61. In the measured gas flow section, the gas inlet 10 is a portion open to the external space, and the measured gas enters the sensor element 101 from the external space through the gas inlet 10. The first diffusion rate control section 11 is a portion that applies a predetermined diffusion resistance to the measured gas entering from the gas inlet 10. The buffer space 12 is a space provided to guide the measured gas introduced from the first diffusion rate control section 11 to the second diffusion rate control section 13. The second diffusion rate control section 13 is a portion that applies a predetermined diffusion resistance to the measured gas introduced from the buffer space 12 to the first internal cavity 20. When the measured gas is introduced from the outside of the sensor element 101 into the first internal cavity 20, the measured gas that rapidly enters the sensor element 101 from the gas inlet port 10 due to the pressure fluctuation of the measured gas in the external space (when the measured gas is the exhaust gas of the internal combustion engine, it is the pulsation of the exhaust pressure) is not directly introduced into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure fluctuation of the measured gas is eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. As a result, the pressure fluctuation of the measured gas introduced into the first internal cavity 20 is almost negligible. The first internal cavity 20 is provided as a space for adjusting the oxygen partial pressure in the measured gas introduced through the second diffusion rate control unit 13. Such oxygen partial pressure is adjusted by operating the main pump unit 21. The main pump unit 21 is an electrochemical pump unit composed of an inner pump electrode 22, an outer pump electrode 23, a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4 that serve as a current path between these electrodes. The inner pump electrode 22 has: a top electrode portion 22a arranged on substantially the entire surface of the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and the outer pump electrode 23 is arranged on the upper surface of the second solid electrolyte layer 6 in an area corresponding to the top electrode portion 22a in a manner exposed to the outside of the element body 102. The inner pump electrode 22 is formed across: the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that partition the first inner cavity 20, and the isolation layer 5 that constitutes the side wall. Specifically, a top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that constitutes the top surface of the first inner cavity 20, and a bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 that constitutes the bottom surface of the first inner cavity 20, and a side electrode portion (not shown) is formed on the side wall surface (inner surface) of the isolation layer 5 that constitutes the two side wall portions of the first inner cavity 20 in a manner that connects the top electrode portion 22a and the bottom electrode portion 22b, thereby being arranged so that: a tunnel-shaped structure is formed at the arrangement position of the side electrode portion. In the main pump unit 21, a desired voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, so that the pump current Ip0 flows between the inner pump electrode 22 and the outer pump electrode 23 in a positive direction or a negative direction. Thus, oxygen in the first internal cavity 20 can be absorbed into the external space, or oxygen in the external space can be absorbed into the first internal cavity 20. In addition, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, that is, an oxygen partial pressure detection sensor unit 80 for main pump control, 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. By measuring the electromotive force (voltage V0) of the oxygen partial pressure detection sensor unit 80 for main pump control, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20 can be known. In addition, the voltage Vp0 of the variable power supply 24 is feedback-controlled so that the voltage V0 reaches a target value, thereby controlling the pump current Ip0. As a result, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value. The third diffusion rate control unit 30 is a part that applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump unit 21 in the first internal cavity 20 , and guides the gas to be measured to the second internal cavity 40 . The second internal cavity 40 is provided as a space for performing the following processing: the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal cavity 20, and then the oxygen partial pressure of the measured gas introduced through the third diffusion rate control unit 30 is further adjusted by the auxiliary pump unit 50. Thus, the oxygen concentration in the second internal cavity 40 can be kept constant with high accuracy, and therefore, the NOx concentration can be measured with high accuracy in the gas sensor 100. The auxiliary pump unit 50 is an auxiliary electrochemical pump unit composed of an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is an appropriate electrode arranged on the outer peripheral surface of the element body 102), and a second solid electrolyte layer 6, an isolation layer 5, and a first solid electrolyte layer 4. The auxiliary pump electrode 51 has: a top electrode portion 51a that is roughly entirely arranged on the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40. The auxiliary pump electrode 51 is arranged in the second internal cavity 40 in the same tunnel-shaped structure as the inner pump electrode 22 provided in the first internal cavity 20. That is, a top electrode portion 51a is formed on 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 first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40, and a side electrode portion (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b is formed in a tunnel-shaped structure respectively formed on the two wall surfaces of the isolation layer 5 constituting the side wall of the second internal cavity 40. In the auxiliary pump cell 50 , a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23 , thereby allowing oxygen in the atmosphere in the second internal cavity 40 to be absorbed into the external space or oxygen to be absorbed into the second internal cavity 40 from the external space. In addition, in order to control the oxygen partial pressure in the atmosphere within the second internal cavity 40, an electrochemical sensor unit, namely, an auxiliary pump control oxygen partial pressure detection sensor unit 81, is formed by the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the isolation layer 5, the first solid electrolyte layer 4, and the third substrate layer 3. The auxiliary pump unit 50 performs pumping using a variable power supply 52 whose voltage is controlled based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor unit 81. Thus, the oxygen partial pressure in the atmosphere in the second internal cavity 40 is controlled to a low partial pressure that has substantially no effect on the measurement of NOx. At the same time, the pump current Ip1 is used to control the electromotive force of the main pump control oxygen partial pressure detection sensor unit 80. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor unit 80, and the above-mentioned target value of the voltage V0 is controlled to control the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 to be always constant. When used as a NOx sensor, 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. The fourth diffusion rate control unit 60 is a portion that applies a predetermined diffusion resistance to the gas to be measured whose oxygen concentration (oxygen partial pressure) is 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 61. The fourth diffusion rate control unit 60 has the function of limiting the amount of NOx flowing into the third internal cavity 61. The third internal cavity 61 is provided as a space in which the oxygen concentration (oxygen partial pressure) is adjusted in advance in the second internal cavity 40, and then the gas to be measured introduced through the fourth diffusion rate control unit 60 is processed related to the measurement of the nitrogen oxide (NOx) concentration in the gas to be measured. The NOx concentration is measured mainly in the third internal cavity 61 by the operation of the measurement pump unit 41. The measuring pump cell 41 measures the NOx concentration in the measured gas in the third internal cavity 61. The measuring pump cell 41 is an electrochemical pump cell composed of a measuring electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, a separator 5, and a first solid electrolyte layer 4, and the measuring electrode 44 is provided at a position facing the third internal cavity 61 on the upper surface of the first solid electrolyte layer 4. The measuring electrode 44 also functions as a NOx reduction catalyst for reducing NOx present in the atmosphere in the third internal cavity 61. The measuring pump cell 41 can absorb oxygen generated by decomposition of nitrogen oxides (NOx) in the atmosphere around the measuring electrode 44, and the generated amount can be detected as the pump current Ip2. In order to detect the oxygen partial pressure around the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42 constitute an electrochemical sensor unit, that is, a measuring pump control oxygen partial pressure detection sensor unit 82. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the measuring pump control oxygen partial pressure detection sensor unit 82. The gas to be measured introduced into the second internal cavity 40 passes through the fourth diffusion rate control unit 60 under the condition of controlled oxygen partial pressure and reaches the measuring electrode 44 in the third internal cavity 61. Nitrogen oxides (NOx) in the gas to be measured around the measuring electrode 44 are reduced (2NO→N 2 +O 2 ) to generate oxygen. The generated oxygen is pumped by the measurement pump unit 41. At this time, the voltage Vp2 of the variable power supply 46 is controlled so that the voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor unit 82 is constant (target value). The amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxides in the measured gas. Therefore, the concentration of nitrogen oxides in the measured gas is calculated using the pump current Ip2 in the measurement pump unit 41. In addition, if the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detection mechanism in the form of an electrochemical sensor unit, the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around the measuring electrode 44 and the amount of oxygen contained in the reference atmosphere can be detected, thereby also being able to determine the concentration of the NOx component in the measured gas. In addition, the electrochemical sensor unit 83 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 can use the electromotive force (voltage Vref) obtained by the sensor unit 83 to detect the oxygen partial pressure in the measured gas outside the element body 102 of the sensor element 101, specifically around the outer pump electrode 23. In the gas sensor 100 having such a structure, the main pump unit 21 and the auxiliary pump unit 50 are operated to supply the measured gas whose oxygen partial pressure is always kept at a constant low value (a value that has substantially no effect on the measurement of NOx) to the measurement pump unit 41. Therefore, based on the pump current Ip2 that is approximately proportional to the NOx concentration in the measured gas and flows due to the oxygen generated by the reduction of NOx being sucked out from the measurement pump unit 41, the NOx concentration in the measured gas can be known. Here, each electrode 22, 23, 42, 44, 51 is described. The inner pump electrode 22, the auxiliary pump electrode 51, and the measuring electrode 44 each contain: a first noble metal having catalytic activity. As the first noble metal, for example, at least any one of Pt, Rh, Ir, Ru, and Pd can be cited. The outer pump electrode 23 and the reference electrode 42 also contain the first noble metal. The inner pump electrode 22 and the auxiliary pump electrode 51 also contain: a second noble metal that suppresses the catalytic activity of the first noble metal for a specific gas (NOx). As a result, the reducing ability of the inner pump electrode 22 and the auxiliary pump electrode 51 for the NOx component in the measured gas is weakened. As the second noble metal, for example, Au can be cited. The measuring electrode 44 does not contain the second noble metal. As a result, the reducing ability for the NOx component in the measured gas is higher than that of the inner pump electrode 22 and the auxiliary pump electrode 51. The measuring electrode 44 preferably contains at least one of Pt and Rh in the first noble metal, and may also contain Pt and Rh at the same time. The outer pump electrode 23 and the reference electrode 42 also preferably do not contain the second noble metal. Each electrode 22, 23, 42, 44, 51 preferably includes a noble metal and an oxide having oxygen ion conductivity (such as ZrO 2 ) metal ceramic. Each electrode 22, 23, 42, 44, 51 is preferably a porous body. In this embodiment, the inner pump electrode 22 and the auxiliary pump electrode 51 are made of Pt and ZrO containing 1% Au.2 In addition, the outer pump electrode 23 and the reference electrode 42 are made of Pt and ZrO 2 The measuring electrode 44 is made of Pt, Rh and ZrO 2 Porous metal ceramic electrode. The heater unit 70 has a temperature adjustment function of heating and keeping the sensor element 101 warm so as to improve the oxygen ion conductivity of the solid electrolyte of the element body 102. The heater unit 70 includes a heater 71a, a heater insulating layer 71b, and a pressure release hole 71c. The heater 71a is a resistor formed by being sandwiched from the upper and lower sides by the second substrate layer 2 and the third substrate layer 3. The heater 71a generates heat by being supplied by the heater power supply 72, thereby heating and keeping warm the solid electrolyte of the element body 102 of the sensor element 101. In addition, the heater 71a is buried in the entire region from the first internal cavity 20 to the third internal cavity 61, and the entire sensor element 101 can be adjusted to a temperature that activates the solid electrolyte. The heater insulating layer 71b is an insulating layer formed of an insulator such as alumina on the upper and lower surfaces of the heater 71a. The heater insulating layer 71b is formed to obtain electrical insulation between the second substrate layer 2 and the heater 71a, and between the third substrate layer 3 and the heater 71a. The pressure release hole 71 c is provided to penetrate the third substrate layer 3 and the reference gas introduction layer 48 and communicate with the reference gas introduction space 43 , and is formed to alleviate the internal pressure increase associated with the temperature increase in the heater insulating layer 71 b . The gas sensor 100 further includes a control device 95. Figure 3As shown, the control device 95 includes: the above-mentioned variable power supplies 24, 46, 52, the above-mentioned heater power supply 72, and a control unit 96. The control unit 96 is a microprocessor having a CPU 97 and a storage unit 98. The storage unit 98 is a non-volatile memory capable of rewriting information, and can store various programs and various data, for example. The control unit 96 is input with: the voltage V0 of the main pump control oxygen partial pressure detection sensor unit 80, the voltage V1 of the auxiliary pump control oxygen partial pressure detection sensor unit 81, the voltage V2 of the measurement pump control oxygen partial pressure detection sensor unit 82, the voltage Vref of the sensor unit 83, the pump current Ip0 flowing through the main pump unit 21, the pump current Ip1 flowing through the auxiliary pump unit 50, and the pump current Ip2 flowing through the measurement pump unit 41. In addition, the control unit 96 outputs a control signal to the variable power supplies 24, 46, 52, thereby controlling the voltages Vp0, Vp1, and Vp2 output by the variable power supplies 24, 46, and 52, thereby controlling the main pump unit 21, the measurement pump unit 41, and the auxiliary pump unit 50. The control unit 96 outputs a control signal to the heater power supply 72, thereby controlling the power supplied by the heater power supply 72 to the heater 71a. The storage unit 98 also stores target values ​​V0*, V1*, and V2*, which will be described later. The CPU 97 of the control unit 96 controls each pump unit 21, 41, and 50 with reference to these target values ​​V0*, V1*, and V2*. The control unit 96 performs auxiliary pump control processing, that is, controls the auxiliary pump unit 50 so that the oxygen concentration in the second internal cavity 40 reaches the target concentration. Specifically, the control unit 96 performs feedback control on the voltage Vp1 of the variable power supply 52 so that the voltage V1 reaches a constant value (referred to as the target value V1*), thereby controlling the auxiliary pump unit 50. The target value V1* is determined to be a value such that the oxygen concentration in the second internal cavity 40 reaches a predetermined low concentration that has substantially no effect on the measurement of NOx. The control unit 96 performs the main pump control process, that is, controls the main pump unit 21 so that the pump current Ip1 flowing when the auxiliary pump unit 50 adjusts the oxygen concentration of the second internal cavity 40 by the auxiliary pump control process reaches the target current (referred to as the target value Ip1*). Specifically, the control unit 96 sets the target value of the voltage V0 (referred to as the target value V0*) based on the pump current Ip1 so that the pump current Ip1 flowing due to the voltage Vp1 reaches the constant target value Ip1* (feedback control). In addition, the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value V0* (that is, so that the oxygen concentration of the first internal cavity 20 reaches the target concentration). Through this main pump control process, the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion rate control unit 30 into the second internal cavity 40 is always constant. The target value V0* is set to a value such that the oxygen concentration of the first internal cavity 20 is higher than 0% and becomes a low concentration. In addition, the pump current Ip0 flowing in the main pump control process changes according to the oxygen concentration of the measured gas (i.e., the measured gas around the sensor element 101) flowing into the measured gas flow portion from the gas inlet port 10. Therefore, the control unit 96 can also detect the oxygen concentration in the measured gas based on the pump current Ip0. The main pump control process and the auxiliary pump control process are also collectively referred to as the adjustment pump control process. In addition, the first internal cavity 20 and the second internal cavity 40 are also collectively referred to as the oxygen concentration adjustment chamber. The main pump unit 21 and the auxiliary pump unit 50 are also collectively referred to as the adjustment pump unit. The adjustment pump control process is performed by the control unit 96, so that the adjustment pump unit adjusts the oxygen concentration of the oxygen concentration adjustment chamber. The control unit 96 performs a measurement pump control process, that is, controls the measurement pump unit 41 so that the voltage V2 reaches a constant value (referred to as a target value V2*) (that is, so that the oxygen concentration in the third internal cavity 61 reaches a predetermined low concentration). Specifically, the control unit 96 performs feedback control on the voltage Vp2 of the variable power supply 46 so that the voltage V2 reaches the target value V2*, thereby controlling the measurement pump unit 41. Oxygen is sucked out from the third internal cavity 61 by this measurement pump control process. By performing the measurement pump control process, oxygen is sucked out from the third internal cavity 61 in such a manner that the oxygen generated by the reduction of NOx in the measured gas in the third internal cavity 61 is substantially zero. Furthermore, the control unit 96 obtains the pump current Ip2 as a detection value corresponding to the oxygen generated in the third internal cavity 61 from the specific gas (here, NOx), and calculates the NOx concentration in the measured gas based on the pump current Ip2. The storage unit 98 stores a relational expression (for example, a linear function or a quadratic function), a map, etc. as the correspondence between the pump current Ip2 and the NOx concentration. The relational expression or the map can be solved in advance by experiments. The control unit 96 performs a heater control process, that is, outputs a control signal to the heater power supply 72 to control the temperature of the heater 71a to reach a target temperature (e.g., 800° C.). Here, the temperature of the heater 71a can be expressed by a linear function of the resistance value of the heater 71a. In the heater control process, the control unit 96 calculates the resistance value of the heater 71a in the form of a value regarded as the temperature of the heater 71a (a value that can be converted into a temperature), and performs feedback control on the heater power supply 72 in a manner such that the calculated resistance value reaches a target resistance value (a resistance value corresponding to the target temperature). The control unit 96 can obtain, for example, the voltage of the heater 71a and the current flowing through the heater 71a, and calculate the resistance value of the heater 71a based on the obtained voltage and current. The control unit 96 can calculate the resistance value of the heater 71a using, for example, a three-terminal method or a four-terminal method. When the heater power supply 72 supplies power to the heater 71a, for example, the value of the voltage applied to the heater 71a is changed based on the control signal from the control unit 96, thereby adjusting the power supplied to the heater 71a. In addition, including Figure 3 The control device 95 is connected to the electrodes 22, 23, 42, 44, 51, and the heater 71a, including the variable power supplies 24, 46, 52 and the heater power supply 72, etc., through the corresponding conductive parts 74. The plurality of conductive parts 74 each include a connector electrode 75 and a lead part 76 for electrically connecting the corresponding electrodes and the connector electrode 75. Figure 4 In FIG. 1 , all of the plurality of connector electrodes 75 are shown in the figure, but regarding the lead portions 76 , only the lead portions 76 corresponding to the measuring electrodes 44 are shown in the figure. The plurality of connector electrodes 75 function as terminals for electrically connecting the sensor element 101 to the outside. Figure 4As shown in FIG. 1 , a plurality of connector electrodes 75 are disposed on the rear end side of the first surface 102a (upper surface) or the second surface 102b (lower surface) of the element body 102 of the sensor element 101. Specifically, the plurality of connector electrodes 75 are connector electrodes 75a to 75d disposed on the rear end side of the first surface 102a of the element body 102 in order from the left, and connector electrodes 75e to 75h disposed on the rear end side of the second surface 102b of the element body 102 in order from the left. The connector electrodes 75a to 75d and 75h are connected (electrically connected) to the measuring electrode 44, the outer pump electrode 23, the auxiliary pump electrode 51, the inner pump electrode 22, and the reference electrode 42 via corresponding lead portions 76, respectively. The connector electrodes 75e to 75g are connected to the heater 71a via corresponding lead portions 76, respectively. Here, we use Figure 4 and Figure 5 , the details of the measuring electrode 44 and the corresponding conductive portion 74 (connector electrode 75a and lead portion 76) are described. Figure 2 Although not shown in the figure, in the element body 102, an airtight adhesive layer is provided between two layers adjacent to each other in the stacking direction (vertical direction) of each layer 1 to 6. Therefore, the two layers adjacent to each other are bonded by the corresponding adhesive layer. Each adhesive layer preferably has oxygen ion conductivity like each layer 1 to 6. In the present embodiment, each adhesive layer uses a ceramic having the same zirconium dioxide as each layer 1 to 6 as a main component. Figure 5 As shown, the adhesive layer 7 among the adhesive layers bonds the first solid electrolyte layer 4 and the separator 5. The adhesive layer 7 covers almost all of the upper surface of the first solid electrolyte layer 4 except for the measured gas flow parts such as the buffer space 12, the first internal cavity 20, and the second internal cavity 40. The measuring electrode 44 is provided at a position facing the third internal cavity 61 on the upper surface of the first solid electrolyte layer 4. The lead portion 76 corresponding to the measuring electrode 44 includes an inner lead portion 77 and a side lead portion 78. The inner lead portion 77 is arranged inside the element body 102, and is connected (electrically connected) to the measuring electrode 44 and the side lead portion 78. Specifically, the inner lead portion 77 includes first to fourth portions 77a to 77d. The first portion 77a is arranged at a position facing the third internal cavity 61 on the upper surface of the first solid electrolyte layer 4. The right end of the first portion 77a is connected to the measuring electrode 44, and the first portion 77a extends linearly along the left-right direction to the left side of the third internal cavity 61. The right end of the second portion 77b is connected to the left end of the first portion 77a, and the second portion 77b extends linearly along the left-right direction to a position closer to the left end of the element body 102. The front end of the third portion 77c is connected to the left end of the second portion 77b, and the third portion 77c extends linearly along the front-back direction to the vicinity of the rear end of the element body 102. The right end of the fourth portion 77d is connected to the rear end of the third portion 77c, and the fourth portion 77d extends linearly along the left-right direction to the left end of the element body 102. The left end of the fourth portion 77d reaches (is led to) the third surface 102c (left end surface) of the element body 102, is covered by the side lead portion 78, and is connected thereto. The inner lead portion 77 is a conductor whose main component is a noble metal such as platinum (Pt) or a high melting point metal such as tungsten (W) and molybdenum (Mo). The inner lead portion 77 is preferably a metal ceramic conductor containing a noble metal or a high melting point metal and zirconium dioxide, which is the same as the main component of the first solid electrolyte layer 4. The outer periphery of the inner lead portion 77 except the entirety of the second and third portions 77b and 77c and the left end portion of the fourth portion 77d is surrounded by a lead insulating layer 79. The lead insulating layer 79 insulates the portion of the inner lead portion 77 surrounding the outer periphery from the first solid electrolyte layer 4 and the separator 5. In addition, the outer periphery of the left end portion of the fourth portion 77d is not surrounded by the lead insulating layer 79. Thus, when manufacturing the sensor element 101, it is possible to suppress: the outer periphery of the left end portion of the fourth portion 77d is surrounded by the lead insulating layer 79, thereby suppressing: the connection (electrical conduction) between the left end of the fourth portion 77d and the side lead portion 78 is inhibited. The lead insulating layer 79 is a ceramic insulator such as alumina. The side lead portion 78 is substantially in the shape of a rectangular parallelepiped, and is disposed on the rear end side of the third surface 102c of the element body 102, and is connected to the inner lead portion 77 and the connector electrode 75a. Specifically, the side lead portion 78 is disposed on the third surface 102c in such a manner that the entire left end of the fourth portion 77d of the inner lead portion 77 is covered so that the left end thereof is not exposed to the outside of the sensor element 101. The center portion of the right end surface of the side lead portion 78 is connected (electrically connected) to the left end of the fourth portion 77d. The upper end portion of the right end surface of the side lead portion 78 is connected to the left end surface of the front end portion of the connector electrode 75a. The side lead portion 78 is a conductor whose main component is a noble metal such as platinum (Pt). The side lead portion 78 preferably includes a noble metal and aluminum oxide (Al 2 O 3 ) conductor. The side lead portion 78 is more preferably made of a noble metal, aluminum oxide, and silicon dioxide (SiO 2 ) conductor. In the case where the side lead portion 78 is a conductor containing a noble metal, alumina and silicon dioxide, for example, when the volumes of the noble metal, alumina and silicon dioxide are set to Vp, Va and Vs [Vol %] respectively, it can be set as follows. It can be made to satisfy Va / Vs≤1.5. In addition, it can be made to satisfy Vp / (Va+Vs)≥1.5. In this case, it can be made to satisfy Vp / (Va+Vs)≥2.6. It can be made to satisfy Vp / (Va+Vs)≤19.0. It can be made to satisfy 1.0≤Va / Vs≤1.5. In addition, the side lead portion 78 can satisfy that the ratio of the total mass calculated by converting the oxides of the alkali metals and alkaline earth metals contained therein is less than 0.1wt%. The side lead portion 78 is configured so that when the porosity is Rp [%] and the thickness is Dc [mm], Rp / Dc ≤ 145% / mm is satisfied. When some gas outside the sensor element 101 (element body 102) enters the inside of the element body 102 from the fourth portion 77d of the inner lead portion 77 or the gap between it and the element body 102, it may move to the measuring electrode 44 side along the gap between the inner lead portion 77 or the gap between it and the element body 102 (the gap between the inner lead portion 77 and the lead insulating layer 79, the gap between the lead insulating layer 79 and the element body 102) and reach the measuring electrode 44. Examples of some gas outside the sensor element 101 include volatile organic gas generated by the rubber stopper 157 when the sensor element 101 is exposed to a high temperature environment. When the gas reaches the measuring electrode 44, the oxygen concentration around the measuring electrode 44 may decrease, the voltage V2 detected by the oxygen partial pressure detection sensor unit 82 for measuring pump control may increase, the oxygen sucked out from the third internal cavity 61 by the measuring pump control process may decrease, and the pump current Ip2 may decrease. The decrease in the pump current Ip2 may reduce the detection accuracy of the concentration of the specific gas (NOx). Based on this, in the present embodiment, the side lead portion 78 is configured to satisfy Rp / Dc≤145% / mm. Thus, since the porosity Rp of the side lead portion 78 is small and / or the thickness Dc is large, it is possible to suppress some gas outside the element body 102 from passing through the side lead portion 78. Therefore, it is possible to suppress the gas from entering the inside of the element body 102 from the fourth portion 77d of the inner lead portion 77 or the gap between it and the element body 102, thereby suppressing the gas from reaching the measuring electrode 44. As a result, it is possible to suppress the pump current Ip2 from decreasing, thereby suppressing the reduction in the detection accuracy of the concentration of the specific gas (NOx). The inventors of the present invention have confirmed these facts through experiments, analysis, etc. In addition, by suppressing the gas from reaching the measuring electrode 44, it is possible to suppress the degradation of the measuring electrode 44. The side lead portion 78 is preferably configured to satisfy Rp / Dc ≤ 120% / mm. The side lead portion 78 is preferably configured to satisfy Rp / Dc≥1.5% / mm. Thus, since the porosity Rp of the side lead portion 78 is large and / or the thickness Dc is small, the adhesion between the side lead portion 78 and the third surface 102c of the element body 102 can be improved. As a result, during the firing shrinkage during the manufacture of the sensor element 101, it is possible to suppress the side lead portion 78 from peeling off from the third surface 102c of the element body 102. In addition, it is possible to suppress the side lead portion 78 from peeling off from the third surface 102c of the element body 102 due to the thermal expansion and contraction of the sensor element 101. The inventors of the present invention have confirmed these facts through experiments, analysis, etc. The side lead portion 78 is more preferably configured to satisfy Rp / Dc≥4.5% / mm. The porosity Rp of the side lead portion 78 may be 0.01% or more. The porosity Rp of the side lead portion 78 may be 9.0% or less. The thickness Dc of the side lead portion 78 may be 0.001 mm or more. The thickness Dc of the side lead portion 78 may be 0.080 mm or less. In addition, each porosity such as the porosity Rp of the side lead portion 78 is set to the value derived as follows using an image (SEM image) obtained by observation using a scanning electron microscope (SEM). First, the object to be measured is cut in such a manner that the cross section of the object to be measured (when the side lead portion 78 is the object to be measured, the cross section of the side lead portion 78 along the thickness direction) is set as the observation surface, and the cross-section surface is resin-embedded and polished to prepare an observation sample. Next, the observation surface of the observation sample is photographed with an SEM photograph (secondary electron image, acceleration voltage 15kV, magnification 1000 times, but when the magnification 1000 times is not appropriate, a magnification greater than 1000 times and less than 5000 times), thereby obtaining a SEM image of the object to be measured. Next, the obtained image is subjected to image analysis, and the threshold is determined using the discriminant analysis method (Otsu's binarization) based on the brightness distribution of the brightness data of the pixels in the image. After that, based on the determined threshold, each pixel in the image is binarized into an object part and a pore part, and the area of ​​the object part and the area of ​​the pore part are calculated. Then, the ratio of the area of ​​the pore part to the total area (the total area of ​​the object part and the pore part) is derived as the porosity (unit: %). Next, an example of a method for manufacturing the sensor element 101 of the gas sensor 100 is described below. First, six unfired ceramic green sheets containing an oxygen ion conductive solid electrolyte such as zirconium dioxide as a ceramic component are prepared. A plurality of sheet holes, necessary through holes, etc. for positioning during printing and lamination are formed in advance on the green sheets. In addition, a space that becomes a flow portion of the measured gas is provided in advance on the green sheet that becomes the isolation layer 5 by punching treatment or the like. A space that becomes a reference gas introduction space 43 is also provided in advance on the green sheet that becomes the first solid electrolyte layer 4. Then, corresponding to the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6, pattern printing treatment to form various patterns and drying treatment are performed on each ceramic green sheet. Specifically, the pattern formed is, for example, the pattern of each electrode such as the measuring electrode 44, the inner lead portion such as the inner lead portion 77 connected to each electrode, the lead insulation layer such as the lead insulation layer 79, the connector electrode 75, the reference gas introduction layer 48, the heater portion 70, etc. The pattern printing is performed in the following manner: the pattern forming paste prepared according to the characteristics required by each formation object is applied to the raw sheet using the known screen printing technology. The drying process is also performed using a known drying method. When the pattern printing process and the drying process are completed, the printing process and the drying process of the adhesive paste that becomes the adhesive layer (including the above-mentioned adhesive layer 7) for stacking and bonding the raw sheets corresponding to each layer are performed. Then, the following pressing process is performed: the raw sheets formed with the adhesive paste are positioned using the sheet holes, and they are stacked in a specified order and pressed under specified temperature and pressure conditions, thereby forming them into a stacked body. The stacked body obtained in this way includes a plurality of sensor elements 101. The stacked body is cut and divided into the size of the sensor element 101. Then, a pattern to become the side lead portion 78 is formed on the cross-section of the stacked body, i.e., the portion of the third surface 102c of the element body 102 of the sensor element 101, by screen printing, and the pattern is dried. Then, the stacked body is fired at a predetermined firing temperature to obtain the sensor element 101. Furthermore, when forming the pattern of the inner lead portion 77 and the lead insulating layer 79 on the green sheet that becomes the first solid electrolyte layer 4, for example, the following can be performed. First, a pattern of a portion that covers the lower side of the inner lead portion 77 in the lead insulating layer 79 is formed on the green sheet. Next, a pattern of the inner lead portion 77 is formed. Then, a portion that covers the side and upper side of the inner lead portion 77 in the lead insulating layer 79 is formed. In addition, the pattern forming paste of the side lead portion 78 uses: a paste containing a noble metal such as platinum. The pattern forming paste of the side lead portion 78 preferably uses: a paste containing a noble metal and alumina. The pattern forming paste of the side lead portion 78 more preferably uses: a paste containing a noble metal, alumina and silica. The porosity Rp of the side lead portion 78 can be adjusted as follows: for example, the particle size of the particles contained in the pattern forming paste of the side lead portion 78 is adjusted, the particle size and content ratio of the pore-forming material are adjusted, or the firing temperature and firing time when the laminate is fired are adjusted. The thickness Dc of the side lead portion 78 can be adjusted as follows: for example, the viscosity of the pattern forming paste of the side lead portion 78 is adjusted, or the number of printing times when the pattern is formed is changed. After that, the gas sensor 100 in which the sensor element 101 is embedded is manufactured. For example, the element sealing body 141 is installed on the sensor element 101 to seal and fix it, and the protective cover 130 is installed on the front end side of the element body 102 of the sensor element 101 in the element sealing body 141. In addition, the connector 150 and the lead wire 155 are installed on the rear end side of the element body 102 of the sensor element 101 in a manner that is conductive with the connector electrode 75. Furthermore, the outer cylinder 148 is installed on the rear end side of the element body 102 in the element sealing body 141, and the lead wire 155 is led out from the outer cylinder 148 to the outside, and the outer cylinder 148 is welded and fixed to the main metal fitting 142. Next, the lead wire 155 is passed through the through hole of the rubber stopper 157, the rubber stopper 57 is inserted into the outer cylinder 148, and the outer cylinder 148 is reduced in diameter by riveting to form the riveted parts 148a and 148b, and the rubber stopper 57 and the outer cylinder 148 are fixed. Then, the control device 95 and the sensor element 101 are connected via the lead wire 155. In this way, the gas sensor 100 is obtained. Next, a usage example of the gas sensor 100 is described. The CPU 97 of the control unit 96 first controls the heater power supply 72 to supply power to the heater 71a so that the temperature of the heater 71a reaches the target temperature (e.g., 800°C, etc.). The CPU 97 obtains, for example, a value that can be converted to the temperature of the heater 71a (e.g., the resistance value or current value of the heater 71a), and based on this value, performs feedback control on the heater power supply 72 to control the temperature of the heater 71a. When the temperature of the heater 71a reaches the target temperature (or near the target temperature), the CPU 97 starts to control the above-mentioned pump units 21, 41, and 50 (adjustment pump control processing and measurement pump control processing), and obtains the voltages V0, V1, V2, and Vref from the above-mentioned sensor units 80 to 83. In this state, when the measured gas is introduced from the gas inlet 10, the measured gas passes through the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13 to reach the first internal cavity 20. Next, the oxygen concentration of the measured gas is adjusted in the first internal cavity 20 and the second internal cavity 40 by the main pump unit 21 and the auxiliary pump unit 50, and the adjusted measured gas reaches the third internal cavity 61. Then, the CPU 97 detects the NOx concentration in the measured gas based on the obtained pump current Ip2 and the corresponding relationship stored in the storage unit 98. Here, the correspondence between the components of the present embodiment and the components of the present invention is clarified. The first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the isolation layer 5, and the second solid electrolyte layer 6 of the present embodiment are respectively equivalent to the solid electrolyte layers of the present invention, the element body 102 is equivalent to the element body, the first to fourth surfaces 102a to 102d are equivalent to the side surface, the measuring electrode 44 is equivalent to the inner electrode, the conductive portion 74 is equivalent to the conductive portion, the inner lead portion 77 is equivalent to the inner conductive portion, the connector electrode 75a and the side lead portion 78 are equivalent to the outer conductive portion, and the side lead portion 78 is equivalent to the covering portion. In addition, the protective cover 130 and the sensor assembly 140 are equivalent to the housing, and the rubber stopper 157 is equivalent to the sealing member. In the sensor element 101 provided in the gas sensor 100 of the present embodiment described in detail above, the side lead portion 78 covers the left end of the fourth portion 77d of the inner lead portion 77, and is configured so that when the porosity of the side lead portion 78 is set to Rp [%] and the thickness is set to Dc [mm], Rp / Dc ≤ 145% / mm is satisfied. Thus, it is possible to suppress some gases outside the sensor element 101 (element body 102) such as volatile organic gas generated by the rubber stopper 157 from passing through the side lead portion 78, thereby suppressing the gas from entering the inside of the element body 102 from the fourth portion 77d of the inner lead portion 77 or the gap between the fourth portion 77d and the element body 102, and suppressing the gas from reaching the measuring electrode 44. As a result, it is possible to suppress the pump current Ip2 from decreasing, thereby suppressing the reduction in the detection accuracy of the concentration of the specific gas (NOx). In the sensor element 101 , the side lead portion 78 is configured to satisfy Rp / Dc≦120% / mm, thereby further preventing some gas outside the element body 102 from passing through the side lead portion 78 . In the sensor element 101, the side lead portion 78 is configured to satisfy Rp / Dc ≥ 1.5% / mm. This improves the adhesion between the side lead portion 78 and the third surface 102c of the element body 102. As a result, the side lead portion 78 can be prevented from peeling off from the third surface 102c of the element body 102 during the firing shrinkage during the manufacture of the sensor element 101. In addition, the side lead portion 78 can be prevented from peeling off from the third surface 102c of the element body 102 due to the thermal expansion and contraction of the sensor element 101. Furthermore, in the sensor element 101 , the side lead portion 78 is configured to satisfy Rp / Dc≧4.5% / mm. This can further improve the adhesion between the side lead portion 78 and the third surface 102 c of the element body 102 . The present invention is not limited to the above-described embodiment, and can be implemented in various forms as long as it falls within the technical scope of the present invention. For example, in the above-mentioned embodiment, the side lead portion 78 is composed of one layer, but it is not limited to this. Figure 6 A sensor element 201 according to a modified example of Figure 7 As shown in the sensor element 301 of the modified example, the side lead portion 78 can be replaced by the side lead portions 278 and 378. The side lead portions 278 and 378 are respectively composed of two layers. In addition, the side lead portions 278 and 378 can be composed of three or more layers instead of two layers. Figure 6In the sensor element 201, the side lead portion 278 is generally in the shape of a rectangular parallelepiped, and has a first side lead portion 278a and a second side lead portion 278b. The first side lead portion 278a is in the shape of a rectangular parallelepiped, and is arranged on the third surface 102c (left side surface) of the element body 102 in such a manner that the entire left end of the fourth portion 77d of the inner lead portion 77 is covered so that the left end thereof is not exposed to the outside of the sensor element 201. The second side lead portion 278b is in the shape of a rectangular parallelepiped, and is arranged on the left end surface of the first side lead portion 278a. In this case, the first side lead portion 278a is equivalent to the covering portion of the present invention. Therefore, the first side lead portion 278a can be constructed in the same manner as the side lead portion 78 of the sensor element 101 so as to satisfy Rp / Dc≤145% / mm, etc. Figure 7 In the sensor element 301, the side lead portion 378 is generally in a substantially rectangular parallelepiped shape, and includes a first side lead portion 378a and a second side lead portion 378b. The first side lead portion 378a is in a substantially rectangular parallelepiped shape, and is disposed on the third surface 102c (left side surface) of the element body 102 in such a manner that the fourth portion 77d of the inner lead portion 77 is entirely covered at the left end thereof so that the left end thereof is not exposed to the outside of the sensor element 301. The second side lead portion 378b covers the five surfaces of the first side lead portion 378a except the right end surface, and is in contact with the third surface 102c of the element body 102, thereby being disposed in such a manner that the fourth portion 77d of the inner lead portion 77 and the first side lead portion 378a are not exposed to the outside of the sensor element 301. In this case, the first side lead portion 378a may correspond to the covering portion of the present invention, the second side lead portion 378b may correspond to the covering portion of the present invention, or the entire side lead portion 378 may correspond to the covering portion of the present invention. Therefore, the first side lead portion 378a, the second side lead portion 378b, and the portion of the entire side lead portion 378 that corresponds to the covering portion of the present invention may be configured to satisfy Rp / Dc≤145% / mm, etc., and may be configured in the same manner as the side lead portion 78 of the sensor element 101. In addition, when the entire side lead portion 378 corresponds to the covering portion of the present invention, the porosity Rp may be derived by setting the cross section of the side lead portion 378 along the thickness direction (the cross section including the first side lead portion 378a and the second side lead portion 378b) as the observation surface, observing using an SEM, and using the obtained SEM image. In the above embodiment, the connector electrode 75a is connected to the measuring electrode 44 via the inner lead portion 77 and the side lead portion 78, but the present invention is not limited thereto. Figure 8As shown in the sensor element 401 of the modified example, the element body 102 is replaced by the element body 402, and the inner lead portion 77 and the side lead portion 78 are replaced by the inner lead portion 477 and the through-hole conductor 478. The element body 402 of the sensor element 401 has a through hole 402h. The through hole 402h includes an opening portion that is open on the first surface 102a of the element body 402, and penetrates the isolation layer 5 and the second solid electrolyte layer 6 along the stacking direction (up and down direction). The inner lead portion 477 is arranged between the first solid electrolyte layer 4 and the isolation layer 5 in the same manner as the inside of the element body 402, specifically, the inner lead portion 77 of the sensor element 101. In addition, at least a portion of the inner lead portion 477 is surrounded by a lead insulation layer (not shown) on its outer periphery in the same manner as the inner lead portion 77. The through-hole conductor 478 is disposed in the through-hole 402h via the insulating layer 479, and the lower end is connected to the inner lead portion 477, and the upper end is covered and connected to the connector electrode 75a in a manner that the entire upper end is not exposed to the outside of the sensor element 401. In this case, the connector electrode 75a is equivalent to the outer conductive portion of the present invention and is a covered portion. Therefore, the connector electrode 75a is configured to satisfy Rp / Dc≤145% / mm, etc., and can be configured in the same manner as the side lead portion 78 of the sensor element 101. In the sensor element 401, the connector electrode 75a is composed of one layer, but it may be composed of two or three layers or more. Figure 6 , Figure 7 The side lead portions 278 and 378 of the sensor elements 201 and 301 of the modified examples are considered in the same manner. In the sensor element 401, the upper end of the through-hole conductor 478 is covered by the connector electrode 75, but the present invention is not limited thereto. Fig. 9As shown in the sensor element 501 of the modified example, the connector electrode 75a is replaced by a connector electrode 575a, and the through-hole conductor 478 is replaced by a through-hole conductor 578. The through-hole conductor 578 is arranged in the through-hole 402h via an insulating layer 579, similarly to the through-hole conductor 478, and the lower end is connected to the inner lead portion 477. The connector electrode 575a has a circular hole 575h, and the outer peripheral portion of the hole 575h at the lower end surface of the connector electrode 575a is connected to the outer peripheral portion of the upper end of the through-hole conductor 578. Therefore, the portion other than the outer peripheral portion at the upper end of the through-hole conductor 578 is exposed to the outside of the sensor element 501. In this case, the upper end portion (the range of a predetermined distance in the vertical direction from the upper end) or the entire through-hole conductor 578 may correspond to the covering portion of the present invention, or the entire through-hole conductor 578 may correspond to the covering portion of the present invention. When the upper end of the through-hole conductor 578 corresponds to the covered portion of the present invention, it can be considered that the upper end of the through-hole conductor 578 covers the remaining portion. When the entire through-hole conductor 578 corresponds to the covered portion of the present invention, it can be considered that the entire through-hole conductor 578 covers the portion of the inner lead portion 477 connected to the through-hole conductor 578. The upper end or the entire portion of the through-hole conductor 578 corresponding to the covered portion of the present invention can be configured to satisfy Rp / Dc≤145% / mm, etc., and can be configured in the same manner as the side lead portion 78 of the sensor element 101. The thickness Dc is defined as the length in the shortest direction of the upper end or the entire portion of the through-hole conductor 578 corresponding to the covered portion of the present invention. Specifically, it is defined as the shorter of the radial distance between the outer periphery of the portion of the upper end surface of the through-hole conductor 578 exposed to the outside of the sensor element 501 and the outer periphery of the entire upper end surface, and the length of the upper end or the entire portion of the through-hole conductor 578 in the vertical direction. In addition, the connector electrode 575a can also be configured in the same manner as the side lead portion 78. In this way, it is possible to prevent gas outside the sensor element 501 (element body 102) from passing through the connector electrode 575a, thereby preventing gas from invading the periphery of the through-hole conductor 578, specifically the gap between the through-hole conductor 578 and the insulating layer 579, and the gap between the insulating layer 579 and the through hole 402h. In the above embodiment, the conductive portion 74 corresponding to the measuring electrode 44 is described. However, the conductive portion 74 corresponding to any one of the inner pump electrode 22, the auxiliary pump electrode 51, and the reference electrode 42 may be provided in the same manner. For example, in the case where the conductive portion 74 corresponding to the measuring electrode 44 includes the connector electrode 75a and the lead portion 76 including the inner lead portion 77 and the side lead portion 78, in the case where the conductive portion 74 corresponding to the inner pump electrode 22 includes the connector electrode 75h and the lead portion including the inner lead portion and the side lead portion, the side lead portion may be configured to satisfy Rp / Dc≤145% / mm, etc., and may be configured in the same manner as the side lead portion 78 of the sensor element 101. In the above-mentioned embodiment, the oxygen concentration adjustment chamber has a first internal cavity 20 and a second internal cavity 40, but is not limited to this. For example, the oxygen concentration adjustment chamber may further include other internal cavities, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above-mentioned embodiment, the adjustment pump unit has a main pump unit 21 and an auxiliary pump unit 50, but is not limited to this. For example, the adjustment pump unit may further include other pump units, or one of the main pump unit 21 and the auxiliary pump unit 50 may be omitted. For example, in a case where the oxygen concentration of the measured gas can be sufficiently reduced using only the main pump unit 21, the auxiliary pump unit 50 may be omitted. In the case where the auxiliary pump unit 50 is omitted, as for the control unit 96, only the main pump control process may be performed as the adjustment pump control process. In addition, in the main pump control process, the above-mentioned setting of the target value V0* based on the pump current Ip1 may be omitted. Specifically, a predetermined target value V0 * is stored in advance in the storage unit 98 , and the control unit 96 performs feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value V0 *, thereby controlling the main pump unit 21 . In the above embodiment, the sensor element 101 of the gas sensor 100 includes the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61, but the present invention is not limited thereto. Fig.10 As shown in the sensor element 601 of the modified example, the third internal cavity 61 is not provided. Fig.10 In the sensor element 601 of the modified example, 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 part 11, a buffer space 12, a second diffusion rate control part 13, a first internal cavity 20, a third diffusion rate control part 30, and a second internal cavity 40 are adjacently formed in a sequentially connected manner. In addition, a measuring electrode 44 is arranged on the upper surface of the first solid electrolyte layer 4 in the second internal cavity 40. The measuring electrode 44 is covered by a fourth diffusion rate control part 45. The fourth diffusion rate control part 45 is: made of aluminum oxide (Al2 O 3 ) or other ceramic porous bodies. The fourth diffusion rate control unit 45 plays the role of limiting the amount of NOx flowing into the measuring electrode 44, similarly to the fourth diffusion rate control unit 60 of the above-mentioned embodiment. In addition, the fourth diffusion rate control unit 45 also functions as a protective film for the measuring electrode 44. The top electrode portion 51a of the auxiliary pump electrode 51 is formed to be directly above the measuring electrode 44. Even with the sensor element 601 having such a structure, the NOx concentration can be detected by using the measuring pump unit 41, similarly to the above-mentioned embodiment. Fig.10 In the sensor element 601 , the periphery of the measuring electrode 44 functions as a measuring chamber. That is, the periphery of the measuring electrode 44 functions similarly to the third internal cavity 61 . In the above embodiment, the outer pump electrode 23 has the functions of an electrode paired with the inner pump electrode 22 in the main pump cell 21 (also referred to as an outer main pump electrode), an electrode paired with the auxiliary pump electrode 51 in the auxiliary pump cell 50 (also referred to as an outer auxiliary pump electrode), and an electrode paired with the measurement electrode 44 in the measurement pump cell 41 (also referred to as an outer measurement electrode), but the present invention is not limited thereto. Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, and the outer measurement electrode may be separately provided on the outside of the element body 102 in a manner that contacts the measured gas, different from the outer pump electrode 23. In the above embodiment, the sensor element 101 detects the NOx concentration in the measured gas, but it is not limited to this as long as it can detect the concentration of the specific gas in the measured gas. For example, the concentration of oxides other than NOx can be set as the concentration of the specific gas. In the case where the specific gas is an oxide, as in the above embodiment, the specific gas itself generates oxygen when it is reduced in the third internal cavity 61, so the measurement pump unit 41 can obtain a detection value corresponding to the oxygen (for example, the pump current Ip2) and detect the specific gas concentration. In addition, the specific gas can be a non-oxide such as ammonia. In the case where the specific gas is a non-oxide, by converting the specific gas into an oxide (for example, if it is ammonia, it is converted into NO), the converted gas generates oxygen when it is reduced in the third internal cavity 61, so the measurement pump unit 41 can obtain a detection value corresponding to the oxygen (for example, the pump current Ip2) and detect the specific gas concentration. For example, the inner pump electrode 22 of the first internal cavity 20 acts as a catalyst, and ammonia can be converted into NO in the first internal cavity 20. In the above embodiment, the element body 102 of the sensor element 101 is set as a stacked body having a plurality of solid electrolyte layers (layers 1 to 6), but it is not limited thereto. The element body 102 only needs to include at least one oxygen ion conductive solid electrolyte layer. For example, Figure 2 In the embodiment, the layers 1 to 5 other than the second solid electrolyte layer 6 may be formed of a material other than the solid electrolyte layer (for example, a layer formed of aluminum oxide). In this case, the electrodes of the sensor element 101 may be arranged on the second solid electrolyte layer 6. For example, Figure 2 The measuring electrode 44 in the second solid electrolyte layer 6 can be arranged on the lower surface of the second solid electrolyte layer 6. In addition, as long as the reference gas introduction space 43 is set in the isolation layer 5 instead of being set in the first solid electrolyte layer 4, the reference gas introduction layer 48 is set between the second solid electrolyte layer 6 and the isolation layer 5 instead of being set between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 is set at the lower surface of the second solid electrolyte layer 6 behind the third internal cavity 61. In the above-described embodiment, the control unit 96 sets the target value V0* of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 reaches the target value Ip1* (feedback control), and performs feedback control on the pump voltage Vp0 so that the voltage V0 reaches the target value V0*, but other controls may be performed. For example, the control unit 96 may perform feedback control on the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 reaches the target value Ip1*. That is, the control unit 96 may omit the acquisition of the voltage V0 from the main pump control oxygen partial pressure detection sensor unit 80 and the setting of the target value V0*, and directly control the pump voltage Vp0 based on the pump current Ip1 (or even control the pump current Ip0). In the above-mentioned embodiment, the form of the gas sensor 100 including the sensor elements 101 , 201 , etc. has been described. However, it is obvious that the form of the sensor elements 101 , 201 , etc. used in the gas sensor 100 may be adopted. Example Hereinafter, an example of manufacturing a sensor element will be described as an embodiment. In addition, the present invention is not limited to the following embodiment. Using the above manufacturing method, Figure 2 The sensor element 101 shown, or making Figure 1The gas sensor 100 shown is set as each experimental example. In addition, when manufacturing the sensor element 101, the ceramic green sheet is obtained by mixing zirconium dioxide particles to which 4 mol% of yttrium trioxide as a stabilizer is added, an organic binder and an organic solvent, and molding by tape casting. In addition, the pattern forming paste of the side lead portion 78 uses a paste containing precious metals, aluminum oxide and silicon dioxide. In each experimental example, the porosity Rp of the side lead portion 78 is changed within the range of 0.01% to 9.0%. The change is performed as follows: the particle size of the particles contained in the pattern forming paste of the side lead portion 78 is changed, the particle size or content ratio of the pore-forming material is changed, or the firing temperature or firing time when the laminate is fired is changed. In addition, in each experimental example, the thickness Dc of the side lead portion 78 is changed within the range of 0.001mm to 0.080mm. Fig.11 1 is an explanatory diagram showing the specifications of the sensor element 101 of each experimental example, specifically, the relationship between the thickness Dc [mm] of the side lead portion 78 and the porosity Rp [%], and Rp / Dc [% / mm]. In the evaluation test 1 described later, the rubber stopper 157 treated in a manner not to generate volatile organic gas was used to produce the sensor element 101 by the above-mentioned manufacturing method. Figure 1 The gas sensor 100 shown is used as a reference gas sensor. In the reference gas sensor, the porosity Rp of the side lead portion 78 is set to 1.0%, and the thickness Dc is set to 0.020 mm. [Evaluation Test 1] An evaluation test of the detection accuracy of the pump current Ip2 was conducted for the reference gas sensor and the gas sensor 100 of each experimental example. First, the reference gas sensor and the gas sensor 100 of each experimental example were installed in the piping in such a manner that the front end side of the element body 102 of the sensor element 101 protruded into the piping, and a temperature sensor was installed on the rubber stopper 157. Next, the heater control process was started to raise the heater 71a to 800°C. Then, a gas obtained by burning a mixture of liquefied petroleum gas (LPG) and air with a burner was used as the measured gas and circulated in the piping. At this time, the flow rates of LPG and air were adjusted so that the air-fuel ratio λ=1.05 and the temperature of the measured gas reached 740°C. In addition, the inventor of the present invention confirmed in advance through another experiment and analysis that the NOx concentration of the measured gas reached approximately 100 ppm in this case. While the measured gas is flowing through the pipe, the pump control process for adjustment and the pump control process for measurement are executed, and the pump current Ip2 is detected for 2 hours. The value obtained by converting the pump current Ip2 of the reference gas sensor into the NOx concentration [ppm] is used as the reference value, and the value obtained by converting the pump current Ip2 of the gas sensor 100 of each experimental example into the NOx concentration [ppm] is used as the evaluation object value. For the gas sensor 100 of each experimental example, the concentration deviation is calculated by subtracting the evaluation object value from the reference value at each time. When the maximum value of the concentration deviation is 7ppm or less, it is set to very good (A), when the maximum value of the difference exceeds 7ppm and is less than 15ppm, it is set to good (B), and when the maximum value of the difference is more than 15ppm, it is set to poor (F). In addition, since the reference gas sensor is processed in a manner that does not generate volatile organic gas as described above, it is assumed that the reference value of the reference gas sensor at each time is not easily affected by Rp / Dc [% / mm]. [Evaluation Test 2] A thermal expansion and contraction test was conducted on each experimental example to evaluate the peeling resistance of the side lead portion 78 from the third surface 102c of the element body 102. Specifically, the gas sensor 100 was placed in a heating and cooling furnace, and the gas sensor 100 was placed at -40°C for 15 minutes and then at 200°C for 15 minutes as one cycle, and this cycle was repeated 600 times. Next, the gas sensor 100 was taken out of the heating and cooling furnace, and the measurement electrode 44 and the connector electrode 75a were investigated to see whether they were conductive via the side lead portion 78. If there was such conductivity, the side lead portion 78 was investigated to see whether they were peeled off from the third surface 102c of the element body 102. Fig.12 and Fig.131 is an explanatory diagram for explaining a method for checking whether the side lead portion 78 and the third surface 102c of the element body 102 are separated. First, the sensor element 101 is placed along Fig.12 Cut off with the thick dashed line. Fig.12 The thick dotted line in FIG. 1 is a line that passes through the center of the side lead portion 78 in the front-rear direction and divides the sensor element 101 into the front end side and the rear end side. Fig.13 The sensor element 101 is then imaged using a SEM at a magnification of 500 times. Fig.13 The five thick solid lines in the figure were observed, and the SEM was used at a magnification of 3000 times. Fig.13 Observe the 5 thick dotted frames in the figure. The 5 thick solid frames and the 5 thick dotted frames are determined in a manner that includes the boundary between the side lead portion 78 and the third surface 102c of the component body 102. When a portion where the distance between the side lead portion 78 and the third surface 102c of the component body 102 is greater than 0.020 mm is confirmed in at least 1 of the 10 locations, it is set as peeling, and when a portion where the distance is greater than 0.020 mm is not confirmed in all locations, it is set as no peeling. Regarding each experimental example, when the measuring electrode 44 and the connector electrode 75a are not conductive via the side lead portion 78, it is set as not possible (F), when there is such conduction but there is peeling between the side lead portion 78 and the third surface 102c of the component body 102, it is set as good (B), and when there is no peeling between the side lead portion 78 and the third surface 102c of the component body 102, it is set as very good (A). As a result of the evaluation test 1, in each experimental example, Fig.11 In the range to the upper left of the solid line La, the evaluation is not acceptable (C), on the contrary, the range between the solid line La and the dotted line Lb (a part of which is the same as the solid line La) is good (B), and the range to the lower right of the dotted line Lb is very good (A). That is, as the result of the evaluation test 1, in each experimental example, the evaluation is not acceptable in the range of Rp / Dc>145% / mm, on the contrary, the evaluation is good in the range of 120% / mm<Rp / Dc≤145% / mm, and the evaluation is very good in the range of Rp / Dc≤120% / mm. Therefore, it can be seen that in each experimental example, in the range of Rp / Dc≤145% / mm, it is possible to suppress the pump current Ip2 from becoming smaller due to the volatile organic gas generated by the rubber plug 157, thereby suppressing the reduction in the detection accuracy of the concentration of the specific gas (NOx). Furthermore, it is found that in each experimental example, in the range of Rp / Dc≤120% / mm, the pump current Ip2 can be further suppressed from decreasing, and the detection accuracy of the concentration of the specific gas (NOx) can be further suppressed from decreasing. As a result of the evaluation test 2, in each experimental example, Fig.11In the range to the lower right of the solid line Lc, the evaluation is unacceptable (C), whereas the range between the solid line Lc and the dotted line Ld (a portion of which is the same as the solid line Lc) is good (B), and the range to the upper left of the dotted line Ld is very good (A). That is, as the result of the evaluation test 2, in each experimental example, the evaluation is unacceptable in the range of Rp / Dc<1.5% / mm, whereas the evaluation is good in the range of 1.5% / mm<Rp / Dc<4.5% / mm, and the evaluation is very good in the range of Rp / Dc≥4.5% / mm. Therefore, it can be seen that in each experimental example, in the range of Rp / Dc≥1.5% / mm, the degree of peeling of the side lead portion 78 from the third surface 102c of the element body 102 due to thermal expansion and contraction of the sensor element 101 of the gas sensor 100 can be suppressed. Furthermore, it is found that in each experimental example, within the range of Rp / Dc ≥ 4.5% / mm, the degree of peeling of the side lead portion 78 from the third surface 102c of the element body 102 due to thermal expansion and contraction of the sensor element 101 of the gas sensor 100 can be further suppressed. Industrial Applicability The present invention can be used for a sensor element for detecting the concentration of a specific gas such as NOx in a measured gas such as exhaust gas of an internal combustion engine, and a gas sensor including the sensor element.

Claims

1. A sensor element for detecting the concentration of a specific gas in a gas to be measured, The sensor element is characterized by comprising: an element body having an oxygen ion conductive solid electrolyte layer and in a columnar shape extending in a longitudinal direction, having a front end and a rear end as both ends along the longitudinal direction, and a side surface as a surface along the longitudinal direction, wherein the front end side is exposed to the measured gas; an inner electrode disposed inside the element body; and Conductive part, The conductive portion includes: an inner conductive portion, which is arranged inside the element body and is conductively connected to the inner electrode; and an outer conductive portion, which has a connector electrode arranged on the rear end side of the side surface, and has a portion arranged on the side surface and / or a portion exposed to the outside of the sensor element on the side surface, and is conductively connected to the inner conductive portion. Regarding the covering portion of the outer conductive portion that covers the inner conductive portion, when the porosity is Rp [%] and the thickness is Dc [mm], Rp / Dc ≤ 145% / mm is satisfied.

2. The sensor element according to claim 1, characterized in that The coated portion satisfies Rp / Dc≤120% / mm.

3. The sensor element according to claim 1 or 2, characterized in that The coated portion satisfies Rp / Dc≥1.5% / mm.

4. The sensor element according to claim 3, characterized in that The coated portion satisfies Rp / Dc≥4.5% / mm.

5. The sensor element according to claim 1 or 2, characterized in that: The porosity Rp is greater than or equal to 0.01% and less than or equal to 9.0%.

6. The sensor element according to claim 1 or 2, characterized in that The thickness Dc is greater than or equal to 0.001 mm and less than or equal to 0.080 mm.

7. The sensor element according to claim 1 or 2, characterized in that: The inner electrode is a measuring electrode for detecting the concentration of the specific gas.

8. The sensor element according to claim 1 or 2, characterized in that The element body is a stacked body in which a plurality of layers including the solid electrolyte layer are stacked in a stacking direction orthogonal to the longitudinal direction. In the stacked body, as the side surfaces, there are: a first surface and a second surface as two end surfaces in the stacking direction, and a third surface and a fourth surface as two end surfaces in a direction orthogonal to the longitudinal direction and the stacking direction, The inner conducting portion includes an inner lead portion led out to the third surface or the fourth surface, The covering portion is a side lead portion that is disposed on the third surface or the fourth surface and covers the inner lead portion.

9. The sensor element according to claim 1 or 2, characterized in that: The element body is a stacked body in which a plurality of layers including the solid electrolyte layer are stacked in a stacking direction orthogonal to the longitudinal direction. In the stacked body, the side surfaces include a first surface and a second surface which are two end surfaces in the stacking direction. The element body has a through hole that penetrates one or more of the plurality of layers along the stacking direction, and the through hole includes an opening portion that is open to the first surface or the second surface on the rear end side of the side surface, The inner conductive portion includes a through-hole conductor disposed in the through-hole, The covering portion is the connector electrode and covers the through-hole conductor.

10. The sensor element according to claim 1 or 2, characterized in that The element body is a stacked body in which a plurality of layers including the solid electrolyte layer are stacked in a stacking direction orthogonal to the longitudinal direction. In the stacked body, the side surfaces include a first surface and a second surface which are two end surfaces in the stacking direction. The element body has a through hole that penetrates one or more of the plurality of layers along the stacking direction, and the through hole includes an opening portion that is open to the first surface or the second surface on the rear end side of the side surface, The covering portion includes a portion of the through-hole conductor that is disposed in the through-hole and exposed to the outside at the opening and is connected to the connector electrode and is exposed to the outside.

11. The sensor element according to claim 1 or 2, characterized in that This sensor element is used in gas sensors. The gas sensor has: the sensor element; a housing having a cylindrical shape extending along the longitudinal direction of the sensor element, having a second front end and a second rear end as both ends along the longitudinal direction, and in which the sensor element is arranged; and A closing member that closes the second rear end side of the housing.

12. A gas sensor, characterized in that: have: The sensor element according to claim 1 or 2; a housing having a cylindrical shape extending along the longitudinal direction of the sensor element, having a second front end and a second rear end as two ends along the longitudinal direction, and having the sensor element disposed therein; as well as A closing member that closes the second rear end side of the housing.

Images