Manufacturing process for sensor element

Abstract

Manufacturing process for a sensor element that detects the concentration of a specific gas contained in a gas of the object being measured, comprising: a manufacturing step for producing a large number of green bodies from ceramic, which is an oxygen-ion-conducting solid electrolyte as its main component; a manufacturing step which includes: a step (a) to form an unfired electrode from a conductive paste on one of the multitude of green bodies, a step (b) to form an unfired electrode conductor and an unfired conductor insulating layer on the same green body as in step (a), wherein the unfired electrode conductor consists of a conductive paste and is to be connected to the unfired electrode, the unburned conductor insulation layer consists of an insulating paste and surrounds at least part of the unburned electrode conductor, and a step (c) to form an unbaked bonding layer from a bonding paste in order to fill at least part of an area without the unbaked conductor insulation layer on the green body subjected to step (b) and to overlap at least part of an edge section of the unbaked conductor insulation layer; a stacking step for stacking the plurality of green bodies including the green body which is subjected to steps (a) to (c) to form a multilayer body in which the unfired electrode conductor is inserted between green bodies; a cutting step to cut out an unfired sensor element from the multilayer body; and a firing step of firing the unfired sensor element to produce a sensor element comprising an electrode formed from the unfired electrode, an electrode lead formed from the unfired electrode lead, a lead insulating layer formed from the unfired lead insulating layer, and a bonding layer formed from the unfired bonding layer.

Description

Technical field

[0001] The present invention relates to a manufacturing process for a sensor element. Technical background

[0002] To date, a gas sensor is known that includes a sensor element capable of detecting the concentration of a specific gas, such as NOx, contained in a sample gas, such as automotive exhaust. For example, PTL 1 discloses a sensor element comprising several oxygen-ion-conducting solid electrolyte layers, an outer pump electrode arranged on the upper layer of a solid electrolyte layer, a measuring electrode arranged within a solid electrolyte layer, and a conductor connected to these electrodes. In this sensor element, the NOx concentration is detected as follows: A sample gas is introduced near the measuring electrode, and oxygen is generated during the reduction of the NOx contained in the gas. The NOx concentration is then detected based on the current flowing between the outer pump electrode and the measuring electrode during the pumping of oxygen.PTL 1 also discloses a manufacturing process for the sensor element. First, several green compacts are produced, and predefined electrode patterns, e.g., of electrodes, are printed onto the green compacts and dried. The multiple green compacts are then stacked on top of each other to form a multilayer body. The multilayer body is cut into units of sensor elements, and the divided sensor element units are fired. This process creates sensor elements.

[0003] It is also known that, to insulate a conductor within a sensor element made of a solid electrolyte layer, an insulating layer is formed on the surface of the solid electrolyte layer, and the conductor is formed on the insulating layer (e.g., PTL 2). PTL 3 describes a sintered body made of laminated aluminum oxide / zirconium oxide with a long lifetime and a sensor element containing the sintered body made of laminated aluminum oxide / zirconium oxide. List of citations Patent literature PTL 1: Japanese unexamined patent application JP 2015 - 180 876 A PTL 2: Japanese unexamined patent application JP 2015 - 227 896 A PTL3: JP 2014 - 10 126 A Brief description of the invention: Technical problem

[0004] In PTL 2, the insulating layer almost completely covers the solid electrolyte layer, and then the conductor is formed on the insulating layer. However, for various reasons, such as the lack of oxygen ion conductivity in an insulating layer, it may be desirable to arrange the insulating layer only around a conductor. To produce such a sensor element, a conductor and an insulating layer can be formed, as shown in Fig. Figure 10 shows that on a green compact 701, which is to be formed into a solid electrolyte layer, an unfired conductor 791 is formed and an unfired insulating layer 792 is formed to surround the unfired conductor 791 ( Fig.10(a)). Then an unfired bonding layer 794 is formed on the green body 701, except for the area where the unfired insulating layer 792 is formed ( Fig. 10(b)). Then another green body 702 with an unfired back bonding layer 797 on its underside is stacked on top of the green body 701 to form a multilayer body ( Fig. 10(c)). The multilayer body is then fired. This produces a sensor element with a conductor 691 made from the unfired conductor 791, an insulating layer 692 made from the unfired insulating layer 792, and a bonding layer 694 made from the unfired bonding layer 794 and the unfired back bonding layer 797 ( Fig. 10(d)). As in Fig.As shown in Figure 10(b), the unfired insulating layer 792 is formed only around the unfired conductor 791 on the green body 701, and the unfired bonding layer 794 is formed on the section of the green body 701 without the unfired insulating layer 792. This makes it possible to produce a sensor element while simultaneously ensuring a uniform height of the pattern formed on the green body 701.

[0005] However, in this manufacturing process, gaps 799 are created between the unfired insulating layer 792 and the unfired bonding layer 794 in the multilayer body, as shown in Fig.Figure 10(c) illustrates this. In the sensor element exposed to fire, gaps 799 may still remain between the insulating layer 692 and the bonding layer 694. With the presence of these gaps 799 in the sensor element, oxygen can flow within them and, during use of the sensor element, reach the vicinity of the electrode, preventing the concentration of a specific gas from being detected with high accuracy.

[0006] The present invention was developed to solve the problem described above. A key objective of the present invention is to suppress the deterioration in the accuracy of detecting the concentration of a specific gas in a sensor element. Solution to the problem

[0007] To solve the main problem described above, the present invention uses the following configurations. Solution to the problem

[0008] A manufacturing process for a sensor element according to the present invention is a manufacturing process for a sensor element that detects the concentration of a specific gas in a gas used as a measuring object. The manufacturing process comprises: a manufacturing step for producing a plurality of green bodies made of ceramic, which is an oxygen-ion-conducting solid electrolyte as the main component;a manufacturing step comprising a step (a) to form an unfired electrode from a conductive paste on one of the plurality of green bodies, a step (b) to form an unfired electrode conductor and an unfired conductor insulating layer on the same green body as in step (a), wherein the unfired electrode conductor consists of a conductive paste and is to be connected to the unfired electrode, the unfired conductor insulating layer consists of an insulating paste and surrounds at least a part of the unfired electrode conductor, and a step (c) to form an unfired bonding layer from a bonding paste to fill at least a part of an area without the unfired conductor insulating layer on the green body subjected to step (b) and to overlap at least a part of an edge section of the unfired conductor insulating layer;a stacking step for stacking the plurality of green bodies, including the green body subjected to steps (a) to (c), to form a multilayer body in which the unfired electrode conductor is inserted between green bodies; a cutting step for cutting out an unfired sensor element from the multilayer body; and a firing step for firing the unfired sensor element to produce a sensor element comprising an electrode formed from the unfired electrode, an electrode conductor formed from the unfired electrode conductor, a conductor insulating layer formed from the unfired conductor insulating layer, and a bonding layer formed from the unfired bonding layer.

[0009] In this manufacturing process, during step (c) of the manufacturing process, the unfired bonding layer is formed such that it overlaps at least part of the edge section of the unfired conductor insulation layer. This makes it less likely that gaps will form between the unfired conductor insulation layer and the unfired bonding layer after the green compacts are stacked. Consequently, it is less likely that gaps will form between a conductor insulation layer and a bonding layer in a fired sensor element. Therefore, it is less likely that, during use of the sensor element, oxygen will flow into gaps and reach the vicinity of an electrode, thereby reducing the accuracy in sensing the concentration of a specific gas within the sensor element.

[0010] In the manufacturing process for a sensor element according to the present invention, in step (c) the unfired bonding layer can be formed such that the maximum Womax value of the overlapping area of ​​the unfired conductor insulation layer and the unfired bonding layer is 20 to 140 µm. With a Womax value of 20 µm or more, it is even less likely that the accuracy in detecting the concentration of a specific gas in the sensor element will decrease. With a Womax value of 140 µm or less, it is possible to reduce distortion that may occur during firing in the sensor element by increasing the width of the overlapping area, i.e., by applying a larger amount of paste to a portion of the green part. In this case, the Womax value can be 120 µm or less, further reducing the occurrence of distortion in the sensor element.

[0011] In the manufacturing process for a sensor element according to the present invention, in step (c), the unfired bonding layer can be formed such that the ratio Womax / Wi of a maximum value Womax [µm] of the width of an overlapping area of ​​the unfired conductor insulation layer and the unfired bonding layer to a width Wi [µm] of the unfired conductor insulation layer in a direction perpendicular to the current flow direction of the unfired electrode conductor is 0.04 to 0.29. With a Womax / Wi ratio of 0.04 or higher, the accuracy in detecting the concentration of a specific gas in the sensor element decreases even less. With a Womax / Wi ratio of 0.29 or lower, it is possible to reduce distortion that can occur during the firing of the sensor element due to an increased width of the overlapping area, i.e., a larger amount of paste applied to a portion of the green part.In this case, the Womax / Wi ratio can be 0.24 or smaller, which can further reduce the occurrence of distortion in the sensor element.

[0012] In the manufacturing process for a sensor element according to the present invention, the unfired conductor insulation layer formed in step (b) can contain a straight section. The straight section is arranged such that the unfired electrode is not located on a line extending longitudinally from the straight section. In step (c), the unfired bonding layer can be formed such that, beneath the edge sections of the straight section, it longitudinally overlaps at least one edge section of the straight section that is positioned closer to the unfired electrode. This configuration makes it less likely that gaps will be produced near the edge section of the conductor insulation layer closer to the electrode. This enhances the effect of minimizing any decrease in detection precision in the sensor element.

[0013] In the manufacturing process for a sensor element according to the present invention, in step (a) an unfired measuring electrode, which is formed into a measuring electrode after firing, can be formed as an unfired electrode. In step (b), an unfired measuring electrode lead, which is connected to the unfired measuring electrode and formed into a measuring electrode lead after firing, can be formed as an unfired electrode lead. It is therefore less likely that oxygen will flow into a gap and reach the vicinity of the measuring electrode during use of the sensor element. If oxygen does flow into a gap and reach the vicinity of the measuring electrode, the accuracy in detecting the concentration of a particular gas is more likely to decrease than if oxygen flows into a gap and reaches the vicinity of another electrode.Due to the formation of the unfired bonding layer to overlap at least part of the edge section of the unfired conductor insulation layer, which surrounds at least part of the unfired measuring electrode conductor, it is even less likely that the accuracy in detecting the concentration of a particular gas in the sensor element will decrease.

[0014] In the manufacturing process for a sensor element according to the present invention, in steps (a) to (c) a plurality of patterns of each of the unfired electrode, unfired electrode conductor, unfired conductor insulation layer, and unfired bonding layer can be formed on the green body, such that the patterns, each corresponding to a sensor element, are arranged in a predetermined direction perpendicular to a longitudinal direction of the sensor element. In the cutting step, a plurality of the unfired sensor elements can be cut from the multilayer body. In the firing step, the plurality of unfired sensor elements can be fired to produce a plurality of sensor elements. This configuration makes it possible to manufacture the plurality of sensor elements at once.

[0015] In this case, in the manufacturing process for a sensor element according to the present invention, in step (b) the plurality of patterns of the unfired conductor insulation layer can be formed such that the patterns corresponding to each sensor element are arranged in the predetermined direction at a first gap. In step (c), the plurality of patterns of the unfired bonding layer can be formed such that the patterns corresponding to each sensor element are arranged in the predetermined direction at a second gap, which is smaller than the first gap. If several patterns of the unfired conductor insulation layer are formed on a green body, such that the patterns corresponding to each sensor element are arranged in the predetermined direction, the gap between the patterns of the unfired conductor insulation layer decreases when the green body shrinks after drying.If, in this case, the gap between the unfired conductor insulation layer and the gap between the unfired bonding layer and the gap between the unfired bonding layer and the unfired conductor insulation layer are set to the same size, misregistration will occur between at least some of the unfired bonding layer patterns and the corresponding unfired conductor insulation layer patterns. With misregistration, the width of the overlapping area between the unfired conductor insulation layer and the unfired bonding layer deviates from the target value. Therefore, it is more likely that sensor elements will be produced that do not maintain sufficient accuracy in determining the concentration of a specific gas. In other words, the yield of the sensor elements will be reduced.In contrast, the multitude of patterns in the unfired bonding layer is formed by using the second gap, which is smaller than the first, to create the patterns in the unfired conductor insulation layer. This reduces misregistration between the patterns of the unfired bonding layer and those of the unfired conductor insulation layer after the green body shrinks. This, in turn, reduces the difference between the actual width of the overlapping area and the target value, thereby improving the efficiency of the sensor elements. Brief description of the drawings Fig. Figure 1 is a schematic sectional view of a gas sensor 100. Fig. 2 is a partial sectional view along line AA of Fig. 1. Fig. Figure 3 is a sectional view along line BB from Fig. 2. Fig.Figure 4 is a view illustrating a green body 204 and several fixture areas 208. Fig. Figure 5 shows top views, which show that 204 individual patterns are formed on the green body. Fig. Figure 6 shows cross-sectional views that reveal that 204 individual patterns are formed on the green body. Fig. Figure 7 shows a first gap section P1 for forming an unfired conductor insulation layer 192 and a second gap section P2 for forming an unfired bonding layer 194. Fig. Figure 8 is a diagram illustrating the representation of the maximum values ​​Womax and pump current values ​​Ip2 after the first to sixth test examples. Fig. Figure 9 is a diagram illustrating the representation of maximum values ​​Womax and delay quantities after the first to sixth experimental examples. Fig.Figure 10 shows views illustrating that a sensor element is manufactured such that an edge section of an unfired insulating layer 792 and that of an unfired bonding layer 794 touch each other. Description of the embodiments

[0016] One embodiment of the present invention will now be described below with reference to the drawings. Fig. Figure 1 is a schematic sectional view of a gas sensor 100 with a sensor element 101 according to an embodiment of the present invention. Fig. Figure 2 is a sectional view of a measuring electrode 44 and a measuring electrode line 91 and their circumferential sections along the line AA of Fig. 1. Fig. Figure 3 is a sectional view along line BB from Fig.2. The gas sensor 100 includes the sensor element 101, which detects the concentration of a specific gas (NOx in this embodiment) in a gas sample. The sensor element 101 is formed in a parallelepiped. The longitudinal direction (left-right direction in Fig. 1) The sensor element 101 is set to the front-back direction. The thickness direction (top-bottom direction in Fig. 1) The orientation of sensor element 101 is set to the up-down direction. The width direction (perpendicular to the front-back direction and to the up-down direction) of sensor element 101 is set to the left-right direction.

[0017] The sensor element 101 consists of six layers: a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6. These layers are, for example, oxygen-ion-conducting solid electrolyte layers made of zirconium dioxide (ZrO2), stacked in this order from the bottom of the drawing. The solid electrolytes forming these six layers are highly gas-tight. The sensor element 101 is manufactured as follows: After ceramic green bodies corresponding to the individual layers have undergone a specific treatment and been printed with circuit patterns, they are stacked on top of each other and fired together to form a single unit.

[0018] At a front end of the sensor element 101 and between the underside of the second solid electrolyte layer 6 and the top side of the first solid electrolyte layer 4, a gas inlet 10, a first diffusion control 11, a buffer chamber 12, a second diffusion control 13, a first interior 20, a third diffusion control 30 and a second interior 40 are formed next to each other in this order, so that they can communicate with each other.

[0019] The gas inlet 10, the buffer chamber 12, the first interior space 20, and the second interior space 40 form a space within the sensor element 101. More precisely, assuming the spacer layer 5 is removed from the sensor element 101, the upper section of this space is defined by the lower section of the second solid electrolyte layer 6, and the lower section of this space is defined by the top surface of the first solid electrolyte layer 4. The side sections of this space are defined by the side faces of the spacer layer 5.

[0020] Each of the first diffusion control 11, the second diffusion control 13, and the third diffusion control 30 is provided as two horizontally extended slots (whose longitudinal direction is perpendicular to the plane of the drawing). The area from the gas inlet 10 to the second interior space 40 is also referred to as the gas passage.

[0021] At a position further from the front end of the sensor element 101 than the gas passage, a reference gas inlet chamber 43 is located between the top surface of the third substrate layer 3 and the bottom surface of the spacer layer 5. The side sections of the reference gas inlet chamber 43 are defined by side surfaces of the first solid electrolyte layer 4. For example, an atmosphere is introduced into the reference gas inlet chamber 43 as the reference gas for measuring the NOx concentration.

[0022] An atmosphere inlet layer 48 is a layer of porous ceramic. The reference gas is introduced into the atmosphere inlet layer 48 via the reference gas inlet chamber 43. The atmosphere inlet layer 48 is designed to cover a reference electrode 42.

[0023] The reference electrode 42 is designed to be inserted between the top surface of the third substrate layer 3 and the first solid electrolyte layer 4. As mentioned previously, the atmosphere inlet layer 48, which communicates with the reference gas inlet chamber 43, is arranged around the reference electrode 42. The oxygen concentration (oxygen partial pressure) in the first chamber 20 and the second chamber 40 can be measured using the reference electrode 42, which will be discussed later.

[0024] During gas passage, the gas inlet 10 to an external chamber is opened. A gas sample is introduced from the external chamber into the sensor element 101 via the gas inlet 10. The first diffusion control 11 applies a predefined diffusion resistance to the gas sample supplied from the gas inlet 10. The buffer chamber 12 is designed to direct the gas sample from the first diffusion control 11 to the second diffusion control 13. The second diffusion control 13 applies a predefined diffusion resistance to the gas sample, which is introduced from the buffer chamber 12 into the first chamber 20. The gas sample from the outside of the sensor element 101 is guided to the first chamber 20 as follows.The gas sampled, which is suddenly introduced into the interior of the sensor element 101 via the gas inlet 10 due to pressure fluctuations in the external space (exhaust gas pressure pulsation if the sampled gas is automotive exhaust), is not directed directly to the first interior space 20. Instead, the gas sampled is directed to the first interior space 20 after the concentration fluctuation of the gas sampled has been neutralized in the first diffusion control 11, the buffer space 12, and the second diffusion control 13. In this way, the fluctuation in the concentration of the gas sampled is rendered almost negligible when it is directed to the first interior space 20. The first interior space 20 is designed as a chamber for adjusting the oxygen partial pressure in the sampled gas input via the second diffusion control 13. The oxygen partial pressure is adjusted by the operation of a main pump cell 21.

[0025] The main pump cell 21 is an electrochemical pump cell consisting of an inner pump electrode 22, an outer pump electrode 23, and the second solid electrolyte layer 6 arranged between these electrodes. The inner pump electrode 22 has a ceiling electrode section 22a that extends almost across the entire underside of the second solid electrolyte layer 6, opposite the first interior space 20. The outer pump electrode 23 is located on the top side of the second solid electrolyte layer 6 and extends in an area corresponding to the ceiling electrode section 22a to be exposed to an external space.

[0026] The inner pump electrode 22 is configured to reach the upper and lower solid electrolyte layers (second and first solid electrolyte layers 6 and 4) that define the first interior space 20, with the intervening spacer layer 5 defining the side walls of the first interior space 20. More precisely, the inner pump electrode 22 is formed as follows: The top electrode section 22a is formed on the underside of the second solid electrolyte layer 6, which serves as the top surface of the first interior space 20. A bottom electrode section 22b is formed on the upper side of the first solid electrolyte layer 4, which serves as the bottom surface of the first interior space 20. A side electrode section (not shown) is formed on the side wall surfaces (inner surfaces) of the spacer layer 5, which form both side walls of the first interior space 20.The side electrode section is designed to connect the ceiling electrode section 22a and the floor electrode section 22b. The inner pump electrode 22 is arranged to form a tunnel-like structure at the position where this side electrode section is located.

[0027] The inner pump electrode 22 and the outer pump electrode 23 are designed as porous cermet electrodes (Pt-ZrO2 cermet electrodes with 1% Au). The inner pump electrode 22, which contacts the gas under test, is made of a material with a low capacity to reduce NOx components in the gas under test.

[0028] In the main pump cell 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 to cause a pump current Ip0 to flow between them in either the positive or negative direction. This makes it possible to pump oxygen from within the first interior space 20 into the outer space or vice versa.

[0029] To detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first interior space 20, an electrochemical sensor cell, that is, a main pump controlling oxygen partial pressure detection sensor cell 80, is formed by the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42.

[0030] Measuring the electromotive force V0 in the oxygen partial pressure sensing sensor cell 80, which controls the main pump, makes it possible to determine the oxygen concentration (oxygen partial pressure) in the first chamber 20. By controlling the pump voltage Vp0 from a variable current source 24 with feedback, so that the electromotive force V0 remains constant, the pump current Ip0 is regulated. This allows the oxygen concentration within the first chamber 20 to be maintained at a predetermined constant value.

[0031] After the gas of the object being measured has flowed through the first interior space 20, where the oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump 21, the third diffusion control 30 applies a predetermined diffusion resistance to the gas of the object being measured in order to guide it to the second interior space 40.

[0032] The second chamber 40 is designed as a space for carrying out treatments related to measuring the nitrogen oxide (NOx) concentration in the sample gas from the third diffusion control unit 30. The NOx concentration is primarily measured in the second chamber 40, where the oxygen concentration is controlled by an auxiliary pump cell 50 and also measured by the operation of a measuring pump cell 41.

[0033] After the oxygen concentration (oxygen partial pressure) in the first chamber 20 has been controlled, the oxygen partial pressure in the second chamber 40 is also adjusted via the auxiliary pump cell 50 for the gas flowing into the second chamber 40 using the third diffusion control 30. This allows the oxygen concentration in the second chamber 40 to be maintained at a constant value with high precision, thus enabling highly accurate measurements of the NOx concentration in the gas sensor 100.

[0034] The auxiliary pump cell 50 is an electrochemical auxiliary pump cell consisting of an auxiliary pump electrode 51, the outer pump electrode 23, and the second solid electrolyte layer 6. The auxiliary pump electrode 51 has a ceiling electrode section 51a that extends almost across the entire underside of the second solid electrolyte layer 6, which faces the second interior space 40. The outer pump electrode 23 is not necessarily required to form the auxiliary pump cell 50; alternatively, a suitable electrode can be used outside the sensor element 101.

[0035] The auxiliary pump electrode 51 is arranged in the second chamber 40 such that it forms a tunnel-like structure, similar to the inner pump electrode 22 in the first chamber 20. The ceiling electrode section 51a is formed on the second solid electrolyte layer 6, which defines the ceiling surface of the second chamber 40. A bottom electrode section 51b is formed on the first solid electrolyte layer 4, defining the bottom surface of the second chamber 40. A side electrode section (not shown) is formed on both side wall surfaces of the spacer layer 5, which form the side walls of the second chamber 40, connecting the ceiling electrode section 51a and the bottom electrode section 51b. The auxiliary pump electrode 51, along with the inner pump electrode 22, is made of a material with a low capacity to reduce NOx components in the gas under test.

[0036] In the auxiliary pump cell 50, by applying a desired pump voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere of the second interior space 40 can be pumped into the outer space, or oxygen in the outer space can be pumped into the second interior space 40.

[0037] To control the oxygen partial pressure in the atmosphere of the second interior space 40, an electrochemical sensor cell, i.e., an auxiliary pump controlling oxygen partial pressure sensing sensor cell 81, is formed by the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, and the third substrate layer 3.

[0038] The auxiliary pump cell 50 performs the pumping using a variable current source 52. The variable current source 52 is voltage-controlled based on the electromotive force V1 detected in the oxygen partial pressure sensing sensor cell 81 controlling the auxiliary pump. This makes it possible to control and reduce the oxygen partial pressure in the atmosphere of the second interior space 40 so low that it does not significantly affect the NOx measurements.

[0039] The pump current Ip1 is also used to control the electromotive force of the main pump-controlling oxygen partial pressure sensing sensor cell 80. Specifically, the pump current Ip1 is input as a control signal into the main pump-controlling oxygen partial pressure sensing sensor cell 80 to control the electromotive force V0 of the main pump-controlling oxygen partial pressure sensing sensor cell 80. The electromotive force V0 is controlled such that the slope of the oxygen partial pressure of the gas under test from the third diffusion control 30 into the second chamber 40 remains constant. If the gas sensor 100 is used as a NOx sensor, the oxygen concentration in the second chamber 40 is maintained at a constant value of approximately 0.001 ppm by the functions of the main pump cell 21 and the auxiliary pump cell 50.

[0040] The measuring pump cell 41 measures the NOx concentration contained in the sample gas in the second chamber 40. The measuring pump cell 41 is an electrochemical pump cell consisting of the measuring electrode 44, the outer pump electrode 23, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The measuring electrode 44 is mounted on the top of the first solid electrolyte layer 4 in a position opposite the second chamber 40 and separated from the third diffusion control 30.

[0041] The measuring electrode 44 is a porous cermet electrode. The measuring electrode 44 also serves as a NOx reduction catalyst for the reduction of NOx in the atmosphere of the second interior space 40. The measuring electrode 44 is covered with a fourth diffusion control 45.

[0042] The fourth diffusion control 45 is a porous ceramic film. The fourth diffusion control 45 serves to limit the NOx volume in the measuring electrode 44 and also acts as a protective film for the measuring electrode 44. The measuring pump cell 41 can pump out the oxygen produced by the decomposition of nitrogen oxide in the atmosphere around the measuring electrode 44 in order to measure the volume of oxygen produced as the pump current Ip2.

[0043] To detect the oxygen partial pressure around the measuring electrode 44, an electrochemical sensor cell, i.e., a measuring pump-controlling oxygen partial pressure detection sensor cell 82, is formed by the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44, and the reference electrode 42. A variable current source 46 is controlled based on the electromotive force V2 detected in the measuring pump-controlling oxygen partial pressure detection sensor cell 82.

[0044] The gas flowing into the second chamber 40 reaches the measuring electrode 44 via the fourth diffusion control 45 in the state where the oxygen partial pressure is controlled. The nitrogen oxide contained in the gas around the measuring electrode 44 is reduced (2NO₂ → N₂ + O₂) to produce oxygen. The generated oxygen is pumped out by the measuring pump cell 41. During oxygen pumping, the voltage Vp₂ of the variable current source 46 is controlled such that the electromotive force V₂ detected in the oxygen partial pressure sensor cell 82, which controls the measuring pump, remains constant. The volume of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas. The nitrogen oxide concentration in the gas is thus calculated using the pump current Ip₂ detected by the measuring pump cell 41.

[0045] Alternatively, the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 can be combined to form an oxygen partial pressure detector as an electrochemical sensor cell. It is then possible to detect the electromotive force based on the difference between the volume of oxygen contained in the reference atmosphere and the volume generated by the reduction of NOx components in the atmosphere around the measuring electrode 44. This also makes it possible to determine the concentration of NOx components in the gas under test.

[0046] An electrochemical sensor cell 83 is formed by the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. Using the electromotive force Vref generated by this sensor cell 83, the oxygen partial pressure in the gas of the sample outside the sensor can be detected.

[0047] In the gas sensor 100 configured as described above, the gas to be measured is supplied to the measuring pump cell 41, while the oxygen partial pressure is kept at a constantly low value (which does not significantly affect the NOx measurements) by the operation of the main pump cell 21 and the auxiliary pump cell 50. The pump current Ip2 flows through the pumping out of the oxygen produced by NOx reduction in the measuring pump cell 41 and is essentially proportional to the NOx concentration in the gas to be measured. Based on this pump current Ip2, the NOx concentration in the gas to be measured can be detected.

[0048] The sensor element 101 also includes a heating unit 70 for improving the oxygen ion conductivity of the solid electrolytes. The heating unit 70 serves to adjust the temperature of the sensor element 101 by heating and maintaining it at that temperature. The heating device 70 includes a heating element 72, a through-hole 73, a heating insulation layer 74, and a pressure distribution hole 75.

[0049] The heating device 72 is an electrical resistor arranged in a top-bottom direction between the second substrate layer 2 and the third substrate layer 3. The heating device 72 is connected to a lower terminal pad 86 via the through-hole 73. When current is supplied from the outside via the lower terminal pad 86, the heating device 72 generates heat to warm and maintain the temperature of the solid electrolytes forming the sensor element 101.

[0050] The heating device 72 is concealed along the entire first interior space 20 and the second interior space 40 in order to set the temperature of the entire sensor element 101 to a temperature at which the solid electrolytes described above can be activated.

[0051] The heating insulation layer 74, which is an insulator made of, for example, aluminum oxide, is formed on the top and bottom surfaces of the heating device 72. The heating insulation layer 74 is formed to provide electrical insulation between the second substrate layer 2 and the heating device 72, as well as between the third substrate layer 3 and the heating device 72.

[0052] The pressure distribution hole 75 is routed through the third substrate layer 3 for communication with the reference gas inlet chamber 43. The pressure distribution hole 75 serves to relieve an increase in internal pressure that accompanies a temperature increase in the heating insulation layer 74.

[0053] An upper connection pad 85 (see Fig. 1) is located at the rear end of the top surface of the second solid electrolyte layer 6. Similarly, the lower connection pad 86 is located at the rear end of the underside of the first substrate layer 1. The upper and lower connection pads 85 and 86 serve as connection electrodes for the electrical connection of the sensor element 101 to the outside. The majority of the (four in this embodiment) upper connection pads 85 and the majority of the (four in this embodiment) lower connection pads 86 are arranged, although they are not shown. One of the upper connection pads 85 is electrically connected to the one shown in the Fig. 2 and Fig.The measuring electrode 44 is connected to the measuring electrode 3 shown via measuring electrode 91 and is also electrically connected to the measuring electrode 44 via measuring electrode 91. Each of the electrodes other than the measuring electrode 44 is also electrically connected to the upper terminal pad 85 or the lower terminal pad 86 via an electrode lead, which is not shown. It is possible to apply a voltage or current to the electrodes (inner pump electrode 22, outer pump electrode 23, reference electrode 42, measuring electrode 44 and auxiliary pump electrode 51) of the sensor element 101 externally and to measure the voltage or current of each of the electrodes via these upper and lower terminal pads 85 and 86. Applying a voltage using the variable current sources 24, 46 and 52 and sensing the pump currents Ip0, Ip1 and Ip2 and the electromotive forces V0, V1, V2 and Vref is also carried out via these upper and lower terminal pads 85 and 86.

[0054] The measuring electrode conductor 91 is a cermet conductor made of zirconium dioxide, the main component of the first solid electrolyte layer 4, and a precious metal, such as platinum, or a high-melting-point metal, such as tungsten or molybdenum. As in Fig.As shown in Figure 2, the measuring electrode lead 91 is located further to the left than the measuring electrode 44 in the sensor element 101. The measuring electrode lead 91 comprises a first straight section 91a, a second straight section 91b, and a third straight section 91c. The first straight section 91a is connected to the left side of the measuring electrode 44 and extends in a left-right direction. The second straight section 91b is connected at its front end to the left end of the first straight section 91a and extends in a front-back direction. The third straight section 91c is connected at its right end to the rear end of the second straight section 91b and extends in a left-right direction.The third straight section 91c is exposed at its end on the left surface of the sensor element 101 and is connected to one of the uppermost terminal pads 85 via a side conductor (not shown) located on the left surface of the sensor element 101. Most of the measuring electrode conductor 91 is surrounded by a conductor insulating layer 92, which is arranged on the first solid electrolyte layer 4.

[0055] The conduction insulating layer 92 is an insulator made of, for example, aluminum oxide and insulates at least part of the measuring electrode lead 91 from the first solid electrolyte layer 4 and the spacer layer 5. The conduction insulating layer 92 has a straight section 93, as shown in Fig.Figure 2 shows the straight section 93. It is arranged such that its longitudinal direction corresponds to the front-back direction. The straight section 93 encloses the measuring electrode lead 91 in such a way that it encompasses part of the first straight section 91a, the entirety of the second straight section 91b, and part of the third straight section 91c. The straight section 93 is arranged along the second straight section 91b, and the measuring electrode 44 is not located on a line extending longitudinally (front-back direction) from the straight section 93. The straight section 93 does not cover part of the right side of the first straight section 91a or part of the left side of the third straight section 91c.This configuration prevents the conductor insulation layer 92 from covering sections where oxygen ion conduction or electrical connection is required, such as the second interior 40, the measuring electrode 44 and the left side of the third straight section 91c during the manufacture of the sensor element 101.

[0056] As in the Fig. 2 and Fig. As shown in Figure 3, a bonding layer 94 is provided on the first solid electrolyte layer 4, which, however, is not in Fig.Figure 1 shows the bonding layer 94 connecting the spacer layer 5 and the first solid electrolyte layer 4. The bonding layer 94 covers most of the top surface of the first solid electrolyte layer 4, except for the gas passages, such as the buffer chamber 12, the first interior space 20, and the second interior space 40. As in layers 1 to 6, the bonding layer 94 preferably exhibits oxygen ion conductivity. In this embodiment, the bonding layer 94 is a ceramic made of zirconium dioxide as its main component, as in layers 1 to 6. A bonding layer, not shown, is arranged not only between the spacer layer 5 and the first solid electrolyte layer 4, but also between adjacent layers of layers 1 to 6.

[0057] A manufacturing process for the sensor element 101 of the gas sensor 100 is explained below. Fig.Figure 4 is a view illustrating a green body 204 and several fixture areas 208. Fig. Figure 5 shows top views, which show that 204 individual patterns are formed on the green body. Fig. Figure 6 shows cross-sectional views that reveal that 204 individual patterns are formed on the green body. Fig. 6(a) is a sectional view along line CC of Fig. 5(a). Fig. 6(b) is a sectional view along line DD of Fig. 5(b). Fig. 6(d) is a sectional view along line EE of Fig. 5(c). Fig. Figure 5 shows some patterns that were formed in a device area 208 of the green body 204. [Manufacturing step]

[0058] In the manufacture of the sensor element 101, a manufacturing step is carried out to produce several ceramic green bodies 200 (zirconium dioxide in this embodiment), the main component of which is an oxygen-ion-conducting solid electrolyte. In this embodiment, the sensor element 101 consists of six layers, i.e., the first to third substrate layers 1 to 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6. Accordingly, six green bodies 200 are produced in conjunction with the six layers. Fig.Figure 4 is shown as one of the six green compacts 200 of the green compact 204, which is formed into the first solid electrolyte layer 4 after firing. In the manufacturing step, pre-made green compacts 200 can be used, or green compacts 200 can be formed. If the green compacts 200 are formed, they can be created as follows: Stabilized zirconium dioxide powder, an organic binder, a plasticizer, and an organic solvent are mixed to form a paste. The green compacts 200 are formed using this paste by the doctor blade method. As shown in Fig.As shown in Figure 4, the green compact 200 is essentially rectangular. For example, pre-punching is performed on the green compact 200 by using a machine press to cut off the four corners in an arc shape and also to create holes in the sheet metal. These sections serve to create patterns or to position the layers to be stacked on top of each other, which will be discussed later. If a particular layer has an internal space, a space (hole) corresponding to this internal space is created in the green compact 200.

[0059] [Manufacturing step] A manufacturing step is then carried out to form patterns corresponding to each of the several sensor elements 101 on one or more green bodies 200, and to dry the formed patterns. Specifically, the patterns for the electrodes, as in the Fig.1 to 3 shown measuring electrode 44, and those for forming the measuring electrode lead 91, the conductor insulation layer 92, the bonding layer 94 and the heating unit 70, as for example in the Fig. 1 to 3 shown. As in Fig. As shown in Figure 4, several device areas 208 are arranged on each of the green bodies 200, each of which is an area in which the patterns corresponding to a sensor element 101 are formed. Individual patterns are formed in each of the device areas 208. The several device areas 208 are arranged in a predetermined direction (left-right direction). Fig.4, the longitudinal direction of the green body 204) is arranged perpendicular to the longitudinal direction (front-to-back direction) of the sensor element 101. In this embodiment, 22 device areas 208 are arranged in the specified direction, and two rows of the 22 device areas 208 are arranged in one direction (longitudinal direction of the sensor element) perpendicular to the specified direction. That is, a total of 44 device areas 208 are arranged. In order to distinguish the 44 device areas 208 from one another, as in Fig. As shown in Figure 4, the 22 device areas 208 are located in the upper section in Fig. 4 from left to right device areas p1 to p22 in Fig. 4 and the 22 device areas 208 in the lower section are device areas p23 to p44 from right to left in Fig. 4. In the several device areas 208, the orientations of the patterns to be formed are also determined. As shown in the enlarged sections in Fig. As shown in Figure 4, the patterns in the device areas p1 to p22 in the upper section are shaped such that the front of the sensor element 101 is in Fig. 4 points downwards. The patterns in the device areas p23 to p44 in the lower area are designed such that the front of the sensor element 101 is in Fig. 4 points upwards. In the enlarged sections in Fig.To illustrate the pattern orientations, the arrows indicate the front, rear, left, and right directions of the sensor elements 101. An unfired measuring electrode 144, which is a pattern for the measuring electrode 44, an unfired measuring electrode lead 191, which is a pattern for the measuring electrode lead 91, and a chamber 143, corresponding to the reference gas inlet chamber 43, are shown. The chamber 143 is a hole formed by punching in the manufacturing step described above. The individual patterns are formed by applying pattern-forming pastes to a green body 200 using a known screen-printing process. The pattern-forming pastes were manufactured according to the properties required for the respective patterns to be formed.

[0060] The manufacturing step comprises the following steps (a) to (c). In step (a), the unfired measuring electrode 144 is formed from a conductive paste on the green body 204, which is one of many green bodies 200. In step (b), the unfired measuring electrode lead 191 and an unfired conductive insulating layer 192 are formed on the same green body 204 as used in step (a). The unfired measuring electrode lead 191 consists of a conductive paste and is connected to the unfired measuring electrode 144. The unfired conductor insulation layer 192 consists of an insulating paste and encloses at least part of the unfired measuring electrode lead 191. After firing, the unfired measuring electrode 144, the unfired measuring electrode lead 191, and the unfired conductor insulation layer 192 are each formed into the measuring electrode 44, the measuring electrode lead 91, and the conductor insulation layer 92, respectively. According to the [reference to the following text] Fig.In the positions and configurations shown in Figures 1 to 3, the unfired measuring electrode 144, the unfired measuring electrode lead 191, and the unfired lead insulation layer 192 are formed in each of the several device areas 208 on the green body 204. In particular, steps (a) and (b) are carried out, for example, as follows. First, step (a) is carried out to form the unfired measuring electrode 144 on the green body 204. Then, step (b) is carried out. Specifically, a lower insulating layer 193a, which is part of the unfired lead insulation layer 192, is formed first, and then the unfired measuring electrode lead 191 is formed on the lower insulating layer 193a. Fig. 5(a) and Fig. 6(a)). As in Fig.As shown in Figure 5(a), the unfired measuring electrode lead 191 includes the first to third straight sections 191a to 191c corresponding to the first to third straight sections 91a to 91c of the measuring electrode lead 91. Then an upper insulating layer 193b is formed on the lower insulating layer 193a and the unfired measuring electrode lead 191 is formed on the lower insulating layer 193a ( Fig. 5(b) and Fig.6(b)). This results in the unfired conductor insulation layer 192 with a straight section 193, consisting of the lower insulating layer 193a and an upper insulating layer 193b. The unfired conductor insulation layer 192 is designed to enclose at least part of the unfired measuring electrode lead 191. In this embodiment, the straight section 193 is formed to enclose part of the first straight section 191a, the entirety of the second straight section 191b, and part of the third straight section 191c. The thickness of the unfired measuring electrode lead 191 is approximately 7 to 17 µm, and the thickness of the unfired conductor insulation layer 192 (total thickness of the lower insulating layer 193a and the upper insulating layer 193b) is approximately 20 to 40 µm, although it is not limited to these ranges.

[0061] In this embodiment, when forming the unfired measuring electrode 144 in step (a), an unfired auxiliary pump electrode 151 is also formed (see Fig. 5(a)) and an unfired main pump electrode (not shown). The unfired auxiliary pump electrode 151b is formed after firing into the bottom electrode section 51b of the auxiliary pump electrode 51. The unfired main pump electrode is formed after firing into the bottom electrode section 22b of the inner pump electrode 22. After the upper insulating layer 193b has been formed in step (b), an unfired fourth diffusion control 145 is formed, which is formed after firing into the fourth diffusion control 45 (see Fig. 5(b)).

[0062] In step (c), an unbaked bonding layer 194 is formed from a bonding paste to fill at least part of the area without the unbaked conductor insulation layer 192 on the green body 204 from step (b) and also to overlap at least part of the edge section of the unbaked conductor insulation layer 192. After firing, the unbaked bonding layer 194 is formed into bonding layer 94 (part of bonding layer 94). For example, the unbaked bonding layer 194 is formed as a pattern with an area where the unbaked bonding layer 194 is formed (indicated by the light hatched section and the dense hatched section in ). Fig.5(c)) and a non-forming area 196 in which the unfired bonding layer 194 is not formed. The non-forming area 196 includes an area in which the gas passage, such as the buffer space 12, the first interior 20, and the second interior 40, is formed, and part of the area in which the unfired line insulation layer 192 is formed on the top layer of the green body 204 (an area other than an overlapping area 195). The unfired bonding layer 194 is formed to fill (cover) most of the top surface of the green body 204 except for the non-forming area 196. The unfired bonding layer 194 is formed to cover the overlapping area 195 (identified by the densely hatched section in Fig. 5(c)) to obtain, wherein the unfired bonding layer 194 overlaps the edge section of the straight section 193 of the unfired conductor insulation layer 192. As in Fig.As shown in Figure 5(c), the unbaked bonding layer 194 is not formed in the section of the green body 204 where the space 143 is formed. However, a hole (space 143) has been formed on the green body 204 to remove the top surface of the green body 204. The unbaked bonding layer 194 does not need to be formed as a pattern to avoid the space 143. In this embodiment, the unbaked bonding layer 194 is formed separately by printing a lower bonding layer 194a and an upper bonding layer 194b several times (twice in this example). In the first print, the lower bonding layer 194a is formed to contact the edge section of the unbaked conductor insulation layer 192 ( Fig. 6(c)). In the second print, the upper bonding layer 194b is formed to overlap at least part of the edge section of the unfired conductor insulation layer 192 ( Fig. 5(c) and Fig.6(d)). As in other patterns, such as unfired measuring electrode 144, the unfired bonding layer 194 is also formed in each of the several device areas 208 on the green body 204.

[0063] In particular, the overlapping area 195 includes a first overlapping area 195a, which overlaps the right edge section of the straight section 193, and a second overlapping area 195b, which overlaps the left edge section of the straight section 193. The overlapping area 195 also includes a third overlapping area 195c, which overlaps the front edge section of the straight section 193, and a fourth overlapping area 195d, which overlaps the rear edge section of the straight section 193. The overlapping area 195 of the unfired conductor insulating layer 192 and the unfired bonding layer 194 is a section in which the unfired conductor insulating layer 192 and the unfired bonding layer 194 overlap each other when viewed in a direction (viewed from above in this embodiment) perpendicular to the surface on which they are formed (top of the green body 204).In this embodiment, the pattern configuration of the unfired conductor insulation layer 192 and the unfired bonding layer 194 is determined such that the width Wo1 of the first overlapping region 195a is substantially uniform at every position in the front-to-back direction. Likewise, the pattern configuration of the unfired conductor insulation layer 192 and the unfired bonding layer 194 is determined such that each of the widths Wo2 to Wo4 of the second to fourth overlapping regions 195b to 195d is substantially uniform at every position in the corresponding direction. The pattern configuration of the unfired conductor insulation layer 192 and that of the unfired bonding layer 194 are also determined such that the widths Wo1 to Wo4 are substantially equal to each other. As mentioned previously, the unfired bonding layer 194 is not formed in a region where the second interior space 40 is formed.Therefore, the unfired bonding layer 194 does not form around the right front region of the straight section 193 (around the first straight section 191a, which is not surrounded by the unfired conductor insulating layer 192 and the unfired measuring electrode 144). In this way, it is not necessary to form the overlapping region 195 in the area where the edge section of the unfired bonding layer 194 and the unfired conductor insulating layer 192 are not adjacent. In this embodiment, for example, the pattern configuration of the unfired conductor insulating layer 192 and the unfired bonding layer 194 is the same for all device regions p1 to p44 on the green body 204. The thickness of the unfired bonding layer 194 (total thickness of the lower bonding layer 194a and the upper bonding layer 194b) is approximately 25 to 45 µm, but is not limited to this range.The thickness of the unfired bonding layer 194 is preferably close to (e.g. 0.8 to 1.2 times as large as the) total thickness of the unfired measuring electrode lead 191 and the unfired conductor insulating layer 192.

[0064] As a result of carrying out the manufacturing step, including steps (a) to (c) described above, the patterns for each of the multiple sensor elements 101 in each of the multiple fixture areas 208, which are arranged in each of the multiple green bodies 200, are formed. The forming sequence of the patterns in the manufacturing step can be changed if necessary, as long as the desired patterns are formed at the desired positions. Regarding the sequence of steps (a) to (c), for example, step (c) is performed after step (b). Step (a) can be performed after step (c), or alternatively, after step (b) and before step (c). In the manufacturing step, drying is carried out after the patterns have been formed as described above. The drying can be carried out using a known drying technique.For example, drying is typically carried out in the atmosphere at a temperature of 75 to 90°C. In this embodiment, drying for a green compact 200 is performed after a single pattern formation. However, drying for a green compact 200 can be performed after multiple pattern formations or after completion of the pattern formation process. [Stack step]

[0065] A stacking step is performed to stack the majority of the green bodies 200, including green body 204, which undergo steps (a) to (c) to form a multilayer body in which the unbaked measuring electrode lead 191 is inserted between the green bodies 200. In this stacking step, unbaked back-side bonding layers, used for bonding the majority of the green bodies 200, including green body 204, are first formed and dried. The unbaked back-side bonding layers are produced, for example, by screen printing, using a bonding layer paste made of the same material as, for example, the unbaked bonding layer 194. The unbaked back-side bonding layer is created by printing a bonding layer paste onto the back side of each green body 200 (e.g.,the surface opposite the surface on which the patterns are formed in the manufacturing step), for example, in the entire area including the multiple fixture areas 208 (fixture areas p1 to p44). The thickness of the unfired back bonding layer is approximately 7 to 17 µm, but is not limited to this area. The forming and drying of the unfired back bonding layers can be carried out in the manufacturing step. After the formation and drying of the unfired back bonding layers, the multiple green bodies 200 are stacked on top of each other and pressed in the top-bottom direction (thickness direction of the sheets) using a known stacking tool, while the positioning of the multiple green bodies 200 is carried out using sheet holes formed in the green bodies 200, thus creating a multi-layered body. This results in, as in . Fig.Figure 6(e) shows a pattern formed on the green body 204, such as the unfired measuring electrode lead 191, inserted and pressed between the green body 204 and a green body 205 with an unfired backside bonding layer 197. The green body 205 is a plate intended to be used as a spacer layer 5 after firing. Another green body 200 is stacked below the green body 204 and above the green body 205, although they are in Fig. 6(e) are not shown. [Cutting step]

[0066] After the formation of the multilayer body in the stacking step, a cutting step is performed to cut out several unfired sensor elements from the multilayer body. In the cutting step, the multilayer body is cut on the green bodies 200 based on the plate holes and cut marks, which are not shown, to cut out several (44 in this embodiment) unfired sensor elements. In this case, the cutting is performed to remove the in Fig. to cut out the device areas 208 shown in the individual green bodies 200 of the multilayer body. [Firing step]

[0067] A firing step is performed to fire the cut, multiple unfired sensor elements under specified conditions. This results in the production of multiple sensor elements 101. After the firing step, the unfired measuring electrode 144, the unfired measuring electrode lead 191, and the unfired conductor insulation layer 192 are formed within an unfired sensor element to form the measuring electrode 44, the measuring electrode lead 91, and the conductor insulation layer 92, respectively. The unfired bonding layer 194 and the unfired reverse bonding layer 197 are formed to form the bonding layer 94. Fig. 6(f)).

[0068] As described above, according to the manufacturing process for the sensor element 101 of this embodiment, in step (c) of the manufacturing step the unbaked bonding layer 194 is formed to form the overlapping area 195 in which the unbaked bonding layer 194 overlaps at least partially with the edge section of the unbaked conductor insulation layer 192 ( Fig. 5(c) and Fig. 6(d)). In contrast to this embodiment, the following case is considered. As in Fig. As shown in Figure 10(b), the unfired bonding layer 794 is configured such that the edge section of the unfired bonding layer 794 touches (does not overlap) the edge section of the unfired insulating layer 792. In this case, the gaps 799 in the multilayer body can be formed as shown in Figure 10(b). Fig. 10(c) shown or in the fired sensor element 101 as in Fig.10(d) is shown. With the presence of the gaps 799 in the sensor element 101, oxygen within the gaps 799 (e.g., oxygen contained in the air filling the gaps 799) can flow during the use of the sensor element 101 and reach the vicinity of an electrode, and the concentration of a specific gas cannot be detected with high accuracy. For example, if oxygen other than that produced by the reduction of nitrogen oxide (i.e., oxygen not originating from a specific gas) flows from the gaps 799 into the vicinity of the measuring electrode 44, the concentration in Fig.The pump current Ip2 or the electromotive force V2 shown in Figure 1 is changed accordingly. This reduces the detection accuracy of the NOx concentration, which is measured using at least one of the pump currents Ip2 and the electromotive force V2. A decrease in detection accuracy is compensated when the auxiliary pump cell 50 pumps oxygen out of the gaps 799. However, the detection accuracy remains low, at least during periods when oxygen is not sufficiently pumped out, such as at the beginning of the use of the sensor element 101. When oxygen flows out of the gaps 799 in this way and reaches the vicinity of the measuring electrode 44, the accuracy in detecting the NOx concentration at the beginning of the use of the sensor element 101 is reduced. That is, the initial stability is reduced.In contrast, in this embodiment, due to the presence of the overlapping area 195, as in . Fig. 5(c) and Fig. 6(d) shown, less likely to produce gaps between (near the boundary between) the unfired conductor insulation layer 192 and the unfired bonding layer 194 after the stacking step ( Fig. 6(e)). Accordingly, it is less likely that gaps will form between the conductor insulation layer 92 and the bonding layer 94 in the fired sensor element 101 ( Fig. 6(f)). It is therefore less likely that oxygen will flow into gaps during the use of the sensor element 101 and reach the measuring electrode 44, so that the initial stability of the sensor element 101 is essentially maintained.

[0069] In step (c), the unfired bonding layer 194 is preferably formed such that the maximum value Womax of the width of the overlapping area 195 of the unfired conductor insulation layer 192 and the unfired bonding layer 194 is 20 to 140 µm. If the overlapping area 195 is present, the maximum value Womax is greater than 0 µm. With a maximum value Womax of 20 µm or more, it is even less likely that the accuracy in detecting the concentration of a specific gas in the sensor element 101 (initial stability in this example) will decrease. With a maximum value Womax of 140 µm or less, it is possible to reduce distortion that may occur during firing in the sensor element 101 by using a larger width of the overlapping area 195, i.e., a larger amount of paste applied to a portion of the green body 204.In this embodiment, the overlapping area 195 is arranged on the left side of the sensor element 101 in the left-right direction. With an increased width of the overlapping area 195, the fired sensor element 101 could warp to the left. However, warping of the fired sensor element 101 is not likely in this embodiment. To more reliably reduce the occurrence of warping in the sensor element 101, the maximum value Womax is preferably 120 µm or less. The maximum value Womax is the greatest width of the overlapping area 195. In this embodiment, each of the widths Wo1 to Wo4 is uniform, and the widths Wo1 to Wo4 are also equal to each other; thus, the widths Wo1 to Wo4 = Womax.

[0070] In step (c), the unfired bonding layer 194 is preferably formed such that the ratio Womax / Wi of the maximum value Womax [µm] to the width Wi [µm] (see Fig.5(c)) of the unfired conductor insulation layer 192 in a direction perpendicular to the current flow direction of the unfired measuring electrode lead 191 is 0.04 to 0.29. The current flow direction of the unfired measuring electrode lead 191 is used as the current flow direction of the longest straight section (second straight section 191b in this embodiment) of the unfired measuring electrode lead 191. Accordingly, in this embodiment, the current flow direction of the unfired measuring electrode lead 191 is the longitudinal direction of the sensor element 101, i.e., the front-to-back direction. The width Wi is a width of the unfired conductor insulation layer 192 in the left-to-right direction perpendicular to the front-to-back direction. If the overlapping area 195 is present, the ratio Womax / Wi is greater than 0 µm. With a Womax / Wi ratio of 0.04 or higher, the accuracy in detecting the concentration of a specific gas in sensor element 101 decreases even less.With a Womax / Wi ratio of 0.29 or less, it is possible to reduce distortion that may occur during firing in the sensor element 101 by increasing the width of the overlapping area 195, i.e., by applying a larger amount of paste to a portion of the green body 204. To further reduce distortion in the sensor element 101, the Womax / Wi ratio is preferably 0.24 or less. The width Wi is, for example, 500 to 650 µm, but is not limited to this range. The width of the unfired measuring electrode lead 191 is, for example, 200 to 300 µm. The width Wi can be 1.0 to 3.25 times the width of the unfired measuring electrode lead 191. The width Wi can be 1.1 times or more the width of the unfired measuring electrode lead 191.

[0071] According to the manufacturing process for the sensor element 101 of this embodiment described in detail above, in step (c) of the manufacturing step, the unfired bonding layer 194 is formed to overlap at least part of the edge section of the unfired conductor insulation layer 192. This makes it less likely that the accuracy in detecting the NOx concentration in the sensor element 101 (initial stability) will decrease. If the maximum value Womax is set to 20 µm or more, it is even less likely that the detection accuracy of the sensor element 101 will decrease. Setting the maximum value Womax to 140 µm or less can reduce the occurrence of distortion in the sensor element 101 during firing. If the Womax / Wi ratio is set to 0.04 or higher, it is even less likely that the detection accuracy of the sensor element 101 will decrease.Setting the Womax / Wi ratio to 0.29 or lower can reduce the occurrence of distortion in sensor element 101 during fire.

[0072] According to the manufacturing process for the sensor element 101, the unfired conductor insulation layer 192 formed in step (b) includes the straight section 193. The straight section 193 is arranged such that the unfired measuring electrode 144 is not located on a line extending longitudinally (front-to-back) from the straight section 193. In step (c), the unfired bonding layer 194 is formed under the edge sections (left edge section and right edge section) along the longitudinal direction of the straight section 193 in order to overlap at least the edge section (right edge section) of the straight section 193 closer to the unfired measuring electrode 144. That is, the unfired bonding layer 194 is formed to create the first overlapping area 195a.Since the distance between an electrode and a gap is smaller, oxygen in the gap is more likely to reach the vicinity of the electrode, and the detection accuracy of the sensor element 101 is more likely to decrease. The unfired bonding layer 194 is designed such that the first overlapping area 195a, which is closer to the unfired measuring electrode 144, is positioned closer than the second overlapping area 195b. Accordingly, gaps are less likely to form near the edge section of the conductor insulation layer 92, which is closer to the measuring electrode 44. This enhances the effect of suppressing the degradation in the detection accuracy of the sensor element 101.

[0073] According to the manufacturing process for the sensor element 101, in step (a) the unfired measuring electrode 144, which is formed into the measuring electrode 44 after firing, is formed as an unfired electrode. In step (b), the unfired measuring electrode lead 191, which is connected to the unfired measuring electrode 144 and is formed into the measuring electrode lead 91 after firing, is formed as an unfired electrode lead. This makes it less likely that a gap will form between the bonding layer 94 and the conductor insulation layer 92, which surrounds the measuring electrode lead 91 connected to the measuring electrode 44. Therefore, it is less likely that oxygen will flow into a gap and reach the vicinity of the measuring electrode 44 during the use of the sensor element 101.When oxygen flows into a gap and reaches the vicinity of the measuring electrode 44, the accuracy in detecting the concentration of a particular gas is more likely to decrease than when oxygen flows into a gap and reaches the vicinity of a different electrode. Due to the formation of the unfired bonding layer 194, which overlaps at least part of the edge section of the unfired conductor insulation layer 192 and surrounds at least part of the unfired measuring electrode conductor 191, it is even less likely that the accuracy in detecting the concentration of a particular gas in the sensor element 101 will decrease.

[0074] According to the manufacturing process for the sensor element 101, in steps (a) to (c) several samples of the unfired measuring electrode 144, the unfired measuring electrode lead 191, the unfired lead insulation layer 192, and the unfired bonding layer 194 are formed on the green body 204 such that the samples, each corresponding to a sensor element 101, are arranged in a predetermined direction (left-right direction) perpendicular to the longitudinal direction (front-back direction) of the sensor element 101. In the cutting step, the several unfired sensor elements are cut out of the multilayer body. In the firing step, the several unfired sensor elements are fired to produce the several sensor elements 101, thus making it possible to produce the several sensor elements 101 at once.

[0075] The present invention is by no means limited to the embodiment described above and can be implemented in various modes without deviating from the technical scope of the present invention.

[0076] In the embodiment described above, no detailed explanation was given of the gap between several patterns used to form a pattern corresponding to a sensor element 101 in each of the device areas 208. This will now be explained below. Fig. Figure 7 shows a first gap section P1 for forming the unfired conductor insulation layer 192 and a second gap section P2 for forming the unfired bonding layer 194. Fig. Figure 7 shows a portion of the device areas p10 to p15 on the green body 204 (area on the back of the sensor element 101). The upper section of Fig.Figure 7 shows the state formed immediately after the formation of the unfired conductor insulation layer 192 (upper insulation layer 193b) (after printing and before drying of the unfired conductor insulation layer 192). The lower section of Fig. Figure 7 shows the state immediately after the formation of the unfired bonding layer 194. If in each of the device areas 208, which are in a predetermined direction (left-right direction in Fig. 4) If different patterns are arranged perpendicular to the longitudinal direction of the sensor element 101, and different patterns are formed according to a sensor element 101, the gaps between the patterns in the specified direction are generally set to the same value (e.g., first gap P1 in Fig.7), regardless of the pattern formed. However, if in step (b) several patterns of the unfired conductor insulation layer 192 are formed such that the patterns corresponding to each sensor element 101 are arranged in the predetermined direction at the first gap section P1, it is preferred that in step (c) several patterns of the unfired bonding layer 194 are formed such that the patterns corresponding to each sensor element 101 are arranged in the predetermined direction at the second gap section P2, which is smaller than the first gap section P1. That is, as shown in device sections p10 to p15, if the gap section of the unfired conductor insulation layer 192 between adjacent device sections 208 in the predetermined direction corresponds to the first gap section P1 (upper section of Fig.7) is, it is preferred that the gap section of the unfired bonding layer 194 between adjacent device areas 208 in the specified direction is the second gap section P2 ( <P1) ist (unterer Abschnitt von Fig.7) If several patterns of the unfired conductor insulation layer 192 are formed on the green body 204, such that the multiple patterns, each corresponding to a sensor element 101, are arranged in the specified direction, and the green body 204 shrinks after drying, the gap between the patterns of the unfired conductor insulation layer 192 becomes smaller than the first gap P1 used to form the patterns. If, in this case, the gap used to form the multiple patterns of the unfired conductor insulation layer 192 and the gap used to form the multiple patterns of the unfired bonding layer 194 are set to the same first gap P1, misregistration occurs between at least some of the multiple patterns of the unfired bonding layer 194 and the corresponding patterns of the unfired conductor insulation layer 192.For example, it is assumed that the unbaked bonding layer 194 on the green body 204 is formed after positioning a screen mask to create the unbaked bonding layer 194 based on the center of the green body 204 in the longitudinal direction. In this case, the height of the misregistration between the contracted unbaked conductor insulation layer 192 and the unbaked bonding layer 194 is greater because the position of the green body 204 extends longitudinally towards the outside. Fig.7. The center of the green body 204 is set longitudinally to a boundary between the device areas p11 and p12. In case of misregistration, the width of the overlapping area (in particular the widths Wo1 and Wo2, which are the widths of the overlapping areas along the specified direction) of the unfired conductor insulation layer 192 and the unfired bonding layer 194 deviates from a target value. This also includes a case in which at least one of the first and second overlapping areas 195a and 195b disappears. If the unfired bonding layer 194 is defined by using the first gap section P1 based on the center of the green body 204 longitudinally as in Fig.As shown in Figure 7, the green compact 204 is displaced outwards relative to the unfired conductor insulation layer 192 due to contraction. Therefore, it is more likely that the width Wo1 will be smaller than the target value and the width Wo2 larger than the target value, since the device area 208 in Fig. 7 is positioned further to the left, i.e., the device area 208 is closer to the device area p22 in Fig. 4 is positioned. Likewise, it is more likely that the width Wo1 will be larger than the target value and the width Wo2 smaller than the target value, since the device area 208 in Fig. 7 is positioned further to the right, i.e., the device area 208 is closer to the device area p1 in Fig.4 is positioned. If the width of the overlap area deviates from the target value, e.g., if the width of the overlap area becomes smaller, it is more likely that sensor elements 101 will be produced that do not sufficiently maintain the accuracy in detecting the concentration of a particular gas. Conversely, if the width of the overlap area becomes larger, the effect described above of reducing the occurrence of distortion in the baked sensor element cannot be sufficiently achieved. That is, the yield of the sensor elements 101 is reduced. In contrast, several patterns of the unbaked bonding layer 194 are formed by using the second gap P2, which is smaller than the first gap P1, to form the patterns of the unbaked conductor insulation layer 192.It is then possible to reduce the misregistration between the patterns of the unfired bonding layer 194 and those of the unfired conductor insulation layer 192 after the contraction of the green body 204. This reduces the difference between the actual value of the width of the overlapping area and the target value, thereby improving the yield of the sensor elements 101.

[0077] The unfired bonding layer 194 in the lower section of Fig.7 is configured to cover most of each device area 208, with the exception of the non-forming area 196. The multiple patterns of the unfired bonding layer 194 formed in the individual device areas 208 are thus interconnected (contacted). The pattern of the unfired bonding layer 194 in each device area 208 includes the non-forming area 196 to avoid sections such as the unfired conductor insulation layer 192. The gap in the non-forming area 196 in the specified direction serves as the gap (second gap P2) between the multiple patterns of the unfired bonding layer 194 in the specified direction. The second gap P2 can be determined experimentally as follows.By checking how much the unfired conductor insulation layer 192 formed by the use of the first gap section P1 has contracted after drying, the second gap section P2 can be adjusted to the same value as the gap section of the unfired conductor insulation layer 192 after drying (gap section for forming the unfired bonding layer 194). For example, the second gap section P2 can have a length [mm] that is 99% or greater and less than 100% of the first gap section P1. The second gap section P2 can be 99.5% or more or 99.9% or more of the first gap section P1.As in the embodiment described above, if the unfired conductor insulation layer 192 is formed separately several times (by forming the lower insulating layer 193a and the upper insulating layer 193b), the gap used to form the final layer (in this example, the gap used to form the upper insulating layer 193b) is used as the first gap P1. As in the embodiment described above, if the unfired bonding layer 194 is formed separately several times (by forming the lower bonding layer 194a and the upper bonding layer 194b), the gap used to form the overlapping area 195 (in particular, the first overlapping area 195a and the second overlapping area 195b with the width along the specified direction) (gap used to form the upper bonding layer 194b in this example) is used as the second gap P2.In this case, the gap used to form one of the layers for the unfired bonding layer 194 is preferably smaller than the first gap P1. For example, the second gap P2 can be used each time a layer for the unfired bonding layer 194 is formed. If the upper bonding layer 194b is formed after the lower bonding layer 194a has dried, the shrinkage caused by the drying of the lower bonding layer 194a is also taken into account, and the gap for forming the upper bonding layer 194b can be set smaller than that for forming the lower bonding layer 194a. As with the formation of the unfired bonding layer 194, when forming patterns on the same green body 200, the gap for a pattern to be formed later can be set smaller.For example, if the lower insulating layer 193a, the unfired measuring electrode lead 191, and the upper insulating layer 193b are formed in this order, the gap between a sample of one of these subsequently formed elements can be set smaller. However, if the width of the lower insulating layer 193a and the upper insulating layer 193b is sufficiently larger than that of the unfired measuring electrode lead 191, a misregistration between the forming positions of the lower insulating layer 193a, the unfired measuring electrode lead 191, and the upper insulating layer 193b due to contraction during drying, for example, has no significant effect on the properties of the sensor element 101.From this point of view, reducing the misregistration between the unfired conductor insulation layer 192 and the unfired bonding layer 194 is more effective in improving the yield of the sensor elements 101 than reducing the misregistration between other patterns.

[0078] During the drying of the formed unfired conductor insulation layer 192, the green body 204 not only stretches longitudinally (left-right direction in the Fig. 4 and Fig. 7), but also in the lateral direction (top-bottom direction in the Fig. 4 and Fig. 7) together. Accordingly, if patterns, where each pattern corresponds to a sensor element 101, can be formed such that they are arranged in several rows (two rows in Fig.4) are arranged in a direction perpendicular to the specified direction, the spacing of the patterns arranged in a direction perpendicular to the specified direction can also be adjusted, i.e., the spacing of the unfired bonding layer 194 can be set smaller than that of the unfired conductor insulation layer 192. For example, the spacing (in the top-bottom direction of Fig. 4) between the device areas p1 to p22 in Fig. 4 formed patterns and those in the device areas p23 to p44 in Fig.The patterns formed for the formation of the unfired bonding layer 194 are set smaller than those for the formation of the unfired conductor insulation layer 192. This can reduce the possibility that the width of the overlapping area (in particular the widths Wo3 and Wo4 of the overlapping areas in the direction perpendicular to the predetermined direction) of the unfired conductor insulation layer 192 and the unfired bonding layer 194 deviates from a target value. This can improve the yield of the sensor elements 101. However, the degree of contraction of the green body 204 in the longitudinal direction is greater than that in the lateral direction. Setting the second gap P2 in the predetermined direction in Fig. Arranging 7 patterns on a smaller area than the first gap P1 is more effective in improving the yield of the sensor elements 101.

[0079] In the embodiment described above, the unbaked bonding layer 194 is configured such that the overlapping region 195 comprises the first to fourth overlapping regions 195a to 195d. However, the formation of the unbaked bonding layer 194 is not limited to this arrangement. The unbaked bonding layer 194 can be formed in another way if it extends at least partially over the edge section of the unbaked conductor insulation layer 192. That is, the unbaked bonding layer 194 can be formed at least for the overlapping region 195. For example, the provision of the fourth overlapping region 195d can be omitted. At least the first and third overlapping regions 195a and 195c can be specified. As already mentioned, since the distance between an electrode and a gap is smaller, the oxygen in the gap reaches the vicinity of the electrode more readily.Thus, among the first to fourth overlapping areas 195a to 195d, the provision of at least the first overlapping area 195a is preferred, then the provision of the third overlapping area 195c is preferable, and then the provision of the second overlapping area 195b is preferred. Alternatively, at least the third overlapping area 195c may be provided.

[0080] In the embodiment described above, the widths Wo1 to Wo4 of the first to fourth overlapping regions 195a to 195d are equal. However, one or more of the widths Wo1 to Wo4 may differ from the other widths Wo1 to Wo4. The width Wo1 of the first overlapping region 195a is essentially uniform at every position in the front-to-back direction. This is only one example, however. For instance, the width Wo1 of the first overlapping region 195a may be larger at a position closer to the unfired measuring electrode 144 (towards the front) and smaller at a position farther from the unfired measuring electrode 144 (towards the back). The mean value of the width Wo1 (mean value of the widths of the first overlapping region 195a at several positions in the front-to-back direction) may be 20 to 140 µm.The width Wo1 of the first overlapping region 195a can be in a range of 20 to 140 µm at any position in the front-to-back direction. The second to fourth overlapping regions 195b to 195d can be modified similarly.

[0081] In the embodiment described above, the Womax / Wi ratio is preferably 0.04 to 0.29. Alternatively, the ratio Wo12max / Wi of the maximum value Wo12max [µm] of the widths Wo1 and Wo2 to the width Wi can be 0.04 to 0.29. The maximum value Wo12max is the maximum value of the widths of the first and second overlapping areas 195a and 195b. In other words, the maximum value Wo12max is the width of the overlapping section of the unbaked bonding layer and the edge section of the unbaked conductor insulation layer 192 in the longitudinal direction of the straight section 193.

[0082] In the embodiment described above, in step (a) the unfired measuring electrode 144, which is formed into measuring electrode 44 after firing, is formed as an unfired electrode. In step (b), the unfired measuring electrode lead 191, which is connected to the unfired measuring electrode 144 and is formed into measuring electrode lead 91 after firing, is formed as an unfired electrode lead. However, these are only examples. The unfired electrode lead formed in step (b) can be any unfired electrode lead that is to be inserted between green bodies in a multilayer body.By providing an overlapping area between the unfired conductor insulation layer surrounding such an unfired electrode lead and the unfired bonding layer, it is less likely that oxygen will flow within a gap and reach the vicinity of an electrode connected to the unfired electrode lead. In this way, it is possible to suppress the decrease in accuracy when detecting the concentration of a specific gas in the sensor element. This is taken into account, for example, the unfired electrode lead that is to be connected to the unfired electrode that, after firing, is formed into the inner pump electrode 22 or the auxiliary pump electrode 51.If an overlapping area is provided between the unfired bonding layer and the unfired conductor insulation layer surrounding the unfired electrode conductor, the desired effect of maintaining the initial stability of the sensor element 101, as described above, is achieved. If oxygen flows from a gap into the vicinity of the inner pump electrode 22 or the auxiliary pump electrode 51, the detection accuracy of the sensor element 101 may decrease and remain constant until the pump cell (main pump cell 21 or auxiliary pump cell 50), including the corresponding inner pump electrode 22 and the auxiliary pump electrode 51, stops pumping out oxygen. However, by providing the overlapping area, it is less likely that the detection accuracy of the sensor element 101 will decrease. Steps (a) to (c) can be performed at each of the multiple electrodes (e.g.,at least two of the measuring electrodes 44, the inner pump electrode 22 and the auxiliary pump electrode 51) and the electrode leads connected to the respective electrodes are connected. With this arrangement, it is less likely that oxygen will flow from a gap to the surroundings of this plurality of electrodes, which enhances the effect on maintaining the detection accuracy of the sensor element 101.

[0083] In the embodiment described above, the individual green body 204 includes the 44 device areas 208, as shown in Fig. Figure 4 illustrates this. However, the number and arrangement of the device areas 208 are not limited to those described above. For example, a green body can have one device area 208.

[0084] In the embodiment described above, the sensor element 101 detects the NOx concentration as the concentration of a specific gas contained in a gas sample. However, this is only one example. For instance, the sensor element 101 can also detect the oxygen concentration as the concentration of a specific gas. Examples

[0085] Examples of specially manufactured sensor elements are explained below. The second through sixth experimental examples correspond to the examples of the present invention, and the first experimental example corresponds to a comparative example. However, the present invention is not limited to the following examples. [First experimental example]

[0086] According to the manufacturing process for sensor element 101 with reference to the Fig. The embodiments discussed in 4 to 6 were those described in Fig.The sensor elements 101 shown in Figure 1 were manufactured and used as the first test example. In the first test example, however, in step (c), the edge section of the unfired conductor insulation layer 192 and that of the unfired bonding layer 194 were in contact with each other, without providing the overlapping area 195 between them. That is, the widths Wo1 to Wo4 = the maximum value Womax = 0 µm and the ratio Womax / Wi was 0 (all were target values, i.e., the set values). The dimensions of the manufactured sensor elements 101 were as follows: The length in the front-back direction was 67.5 mm, the width in the left-right direction was 4.25 mm, and the thickness in the top-bottom direction was 1.45 mm.To produce the sensor elements 101, green compacts 200 were formed by mixing zirconium dioxide particles to which 4 mol% yttrium dioxide (a stabilizer) had been added, an organic binder, and an organic solvent, and by forming the resulting mixture into a ribbon-like shape. A paste consisting of a mixture of 11.2 wt% zirconium dioxide particles to which 4 mol% yttrium dioxide (a stabilizer) had been added, 60 wt% platinum, an organic binder, and an organic solvent was used as the conductive paste for the unfired measuring electrode lead 191. Aluminum oxide powder and a binder solution were mixed in a weight ratio of 1:2 as the insulating paste for the conductor insulating layer 92, and the resulting mixture was adjusted to have a viscosity of 40 Pa·s at room temperature.Zirconium dioxide particles were added as a paste for the bonding layer 94, to which 4 mol% yttrium dioxide, acting as a stabilizer, was added, along with an organic binder and an organic solvent. The resulting mixture was adjusted to have a viscosity of 20 Pa·s at room temperature. The thickness of the unfired measuring electrode lead 191 was 7 to 17 µm, and the thickness of the second straight section 191b of the unfired measuring electrode lead 191 was 9 to 15 µm. The width Wi of the unfired conductor insulating layer 192 was 490 µm, and the combined thickness of the lower insulating layer 193a and the upper insulating layer 193b was 30 µm. The combined thickness of the lower bonding layer 194a and the upper bonding layer 194b was 35 µm. The thickness of the unfired backside bonding layer 197 was 10 µm. As in . Fig.As shown in Figure 7, the second gap P2 of the unfired bonding layer 194 was set smaller than the first gap P1 of the unfired conductor insulation layer 192, so that the actual values ​​of the widths Wo1 to Wo4 would essentially match the target value. Specifically, the unfired conductor insulation layer 192 (lower insulation layer 193a and upper insulation layer 193b) and the unfired measuring electrode conductor 191 were formed with a first gap P1 of 5.27 mm. The unfired bonding layer (lower bonding layer 194a and upper bonding layer 194b) was formed with a second gap P2 of 5.267 mm. To form the patterns of the lower insulating layer 193a, the unfired measuring electrode lead 191, the upper insulating layer 193b, the lower bonding layer 194a and the second overlapping area 195b in this order, drying was carried out during each pattern formation. [Second to sixth experimental examples]

[0087] The sensor elements 101 were manufactured similarly to the first experimental example, except that the target values ​​of the maximum value Womax and the Womax / Wi ratio were varied by changing the configuration of the non-forming area 196 in a screen mask for forming the unfired bonding layer 194. The manufactured sensor elements 101 were used as the second through sixth experimental examples. Specifically, in the second experimental example, the widths Wo1 to Wo3 were set to 30 µm (maximum value Womax) and the Womax / Wi ratio to 0.06. In the third experimental example, the widths Wo1 to Wo3 were set to 60 µm (maximum value Womax) and the Womax / Wi ratio to 0.12. In the fourth experimental example, the widths Wo1 to Wo3 were set to 100 µm (maximum value Womax) and the Womax / Wi ratio to 0.20.In the fifth experimental example, the widths Wo1 to Wo3 were set to the maximum value Womax = 130 µm, and the ratio Womax / Wi was set to 0.27. In the sixth experimental example, the widths Wo1 to Wo3 were set to the maximum value Womax = 150 µm, and the ratio Womax / Wi was set to 0.31. In all experimental examples two through six, the overlapping region 195 did not have a fourth overlapping region 195d. Each of the first interspace segment P1 and the second interspace segment P2 in the second through sixth experimental examples was set to the same value as in the first experimental example. [Assessment regarding initial stability]

[0088] With regard to the first six test examples, the detection accuracy of the sensor elements 101 with respect to a test gas was evaluated, in particular the initial stability of the sensor elements 101. The evaluations were carried out as follows. To raise the temperature of the heating device 72 to a predetermined temperature, a voltage was first applied to the heating unit 70 to cause a current to flow through the heating device 72, and nitrogen was supplied to the gas passage. Then, cells 21, 41, 50, and 80 to 83 were started up. After a specific time interval (240 seconds) following the start of the operation of cells 21, 41, 50, and 80 to 83, the NOx concentration values ​​(values ​​of the pump current Ip2) were measured.Measurements were performed for all 44 sensor elements 101 produced in each of the first six experimental samples, and the mean and standard deviation σ of the pump current Ip2 values ​​were determined for each of the first six experimental samples. If the mean pump current Ip2 was 0.065 µA or less, the initial stability was found to be good (A), and if the mean pump current Ip2 exceeded 0.065 µA, the initial stability was found to be poor (C). The gas supplied to the gas passage was nitrogen, which contained no oxygen. Therefore, the pump current Ip2 would ideally be 0 µA, and if oxygen flowed from a gap within the sensor element 101 to an electrode, the pump current Ip2 would increase. [Assessments regarding the amount of delay in the sensor element]

[0089] The warpage in the sensor elements 101 of the first to sixth test samples was measured. Measurements were performed for all 44 sensor elements 101 produced in each of the first to sixth test samples, and the mean and standard deviation of the warpage were determined for each of the first to sixth test samples. If the mean warpage was 240 µm or less, the evaluation result was set to very good (A). If the mean warpage exceeded 240 µm and was 350 µm or less, the evaluation result was set to good (B). If the mean warpage exceeded 350 µm, the evaluation result was classified as poor (C).

[0090] The target value of the maximum value Womax, the target value of the ratio Womax / Wi, the mean value of the pump current Ip2, the standard deviation of the pump current Ip2, the assessment of the initial stability, the average delay quantity, the standard deviation of the delay quantity and the assessment of the delay quantity after each of the first to sixth test examples are shown in Table 1. Fig. Figure 8 is a diagram illustrating the representation of the target values ​​of the maximum value Womax and the values ​​of the pump current Ip2 after the first to sixth test examples. Fig. Figure 9 is a diagram illustrating the representation of the target values ​​of the maximum value Womax and the delay quantities according to the first to sixth test examples. In the Fig. 8 and Fig. In figure 9, the rhombus represents the mean value, and the horizontal bars above and below the rhombus indicate the values ​​represented by the mean value ± σ. [Table 1] Experimental example 1 2 3 4 5 6 Maximum Womax value [µm] (target value) 0 30 60 100 130 150 Ratio Womax / Wi (setpoint) 0,00 0,06 0,12 0,20 0,27 0,31 Average of Ip2 [µmA] 0,190 0,025 0,026 0,040 0,018 0,020 Standard deviation of Ip2 σ [µmA] 0,086 0,036 0,048 0,025 0,032 0,039 Assessment of initial stability C A A A A A Average amount of distortion [µm] 107,6 109,3 102,8 134,9 270,3 370,0 Standard deviation of the quantity of delay σ [µm] 17,5 16,3 12,3 20,7 21,8 25,1 Assessment of the quantity of delay A A A A B C

[0091] Table 1 and Fig. Figure 8 showed that when comparing the second to sixth test examples, where the target values ​​of the maximum value Womax 0 were exceeded, with the first test example, where the overlapping range 195 was not specified, i.e., the target value of the maximum value Womax 0, the pump current values ​​Ip2 were reduced in all second to sixth test examples, and high initial stability was achieved. Table 1 and Fig. Figure 8 also showed that the standard deviations of the pump current Ip2 of the second to sixth experimental examples were smaller than those of the first experimental example. Table 1 and Fig. Figures 9 showed that, since the target value of the maximum value Womax was smaller, the amount of delay tended to be smaller. Table 1 and Fig.Figure 9 also showed that the distortion amounts in the first five test examples, where the target values ​​for the maximum Womax were 130 µm or less, were smaller than in the sixth test example, where the target values ​​for the maximum Womax exceeded 130 µm. The distortion amounts in the first four test examples, where the target values ​​for the maximum Womax were 100 µm or less, were smaller than in the fifth test example. These results show that, from the perspective of suppressing the detection accuracy of the sensor element 101, the maximum Womax can preferably be 20 µm or more, and more preferably 30 µm or more. Likewise, from the perspective of suppressing the detection accuracy of the sensor element 101, the Womax / Wi ratio can preferably be 0.04 or greater, and more preferably 0.06 or greater.From the perspective of reducing the occurrence of distortion in the sensor element 101, the maximum value Womax can preferably be 140 µm or less, more preferably 130 µm or less, and even more preferably 120 µm or less. The maximum value Womax can also more preferably be 100 µm or less, more preferably 90 µm or less, even more preferably 70 µm or less, and even more preferably 60 µm or less. From the perspective of reducing the occurrence of distortion in the sensor element 101, the ratio Womax / Wi can preferably be 0.29 or less, more preferably 0.27 or less, and even more preferably 0.24 or less. The ratio Womax / Wi can particularly preferably be 0.20 or less, even more preferably 0.18 or less, even more preferably 0.14 or less, and even more preferably 0.12 or less.

[0092] In the first experimental example, the positions in the Fig.In the device areas p1, p11 and p22 shown in Figure 4, several sensor elements 101 were cut off and checked for gaps between the conductor insulation layer 92 and the bonding layer 94 in cross-section and, if applicable, the size of the gaps. The average width of the gaps was 46.7 µm. The widths of the gaps were specifically measured as follows. The straight section 193 of the conductor insulation layer 192 was first cut in cross-section similar to that shown in Figure 4. Fig. The cross-section shown in section 6 was observed. Among the gaps found in the cross-section, the total width of the gaps on the left and right sides (corresponding to the left and right sides in the cross-section) was determined. Fig.6) of the straight section 193 was measured. Then, the value of half the total width was adjusted to the width of the gaps in the sensor element 101. For the third experimental example, the average gap width was calculated similarly and found to be 3.8 µm. This confirmed that gaps between the conductor insulation layer 92 and the bonding layer 94 were less likely in the third experimental example than in the first. In the third experimental example, no gaps were found in the cross-section of some sensor elements 101 (i.e., the gap width was 0 µm). However, in the first experimental example, gaps were found in the cross-section of all sensor elements 101.

[0093] This application is based on the priority of the previous Japanese patent application No. 2016-143044, filed on July 21, 2016, and claims its priority, and its entire contents are incorporated herein by reference. Industrial applicability

[0094] The present invention can be used in the manufacturing industry for sensor elements that detect the concentration of a specific gas, such as NOx, contained in a gas used in the measurement, such as automotive exhaust gases. Reference symbol list 1 first substrate layer 2 second substrate layer 3 third substrate layer 4 first solid electrolyte layer 5 spacer layer 6 second solid electrolyte layer 10 Gas inlet 11 First diffusion control 12 Buffer space 13 Second diffusion control 20 first interior 21 Main pump cell 22 inner pump electrode 22a Ceiling electrode section 22b Ground electrode section 23 external pump electrode 24 variable power source 30 third diffusion control 40 second interior 41 Measuring pump cell 42 Reference electrode 43 Reference gas inlet chamber 44 Measuring electrode 45 fourth diffusion control 46 variable power source 48 Atmosphere intake layer 50 Auxiliary pump cells 51 Auxiliary pump electrode 51a Ceiling electrode section 51b Ground electrode section 52 variable power source 70 heating units 72 Heating device 73 Through hole 74 Heating insulation layer 75 Pressure distribution hole 80 main pump controlling oxygen partial pressure sensing sensor cell 81 Auxiliary pump controlling oxygen partial pressure sensing sensor cell 82 measuring pumps controlling oxygen partial pressure sensing sensor cell 83 sensor cells 85 upper connection pad 86 lower connection pad 91 Measuring electrode lead 91a to 91c first to third even section 92 Conductor insulation layer 93 straight section 94 Bonding layer 100 gas sensor 101 Sensor element Room 143 144 unburned measuring electrode 145 unburned fourth diffusion control 151 unburned auxiliary pump electrode 191 unburned measuring electrode leads 191a to 191c first to third even section 192 unburned conductor insulation layer 193 straight section 193a lower insulating layer 193b upper insulating layer 194 unfired bonding layer 194a lower bonding layer 194b upper bonding layer 195 overlapping area 195a to 195d first to fourth overlapping area 196 non-educational area 197 unfired back bonding layer 200, 204, 205 Greenling 208 Device area p1 to p44 Device area 691 Management 692 Insulating layer 694 Bonding layer 701, 702 Greenling 791 unburned cable 792 unfired insulating layer 794 unfired bonding layer 797 unfired reverse bonding layer 799 gap

Claims

[1] A manufacturing method for a sensor element that detects the concentration of a specific gas contained in a measurement object gas, comprising: a manufacturing step of producing a plurality of green compacts from ceramic, which is an oxygen ion conductive solid electrolyte, as a main component; a manufacturing step including: a step (a) of forming an unfired electrode from a conductive paste on one of the plurality of green compacts, a step (b) of forming an unfired electrode lead and an unfired lead insulating layer on the same green body as in step (a), wherein the unfired electrode lead is made of a conductive paste and is to be connected to the unfired electrode, the unfired wire insulation layer consists of an insulating paste and surrounds at least part of the unfired electrode wire, and a step (c) of forming an unfired bonding layer from a bonding paste to fill at least a part of an area without the unfired wiring insulating layer on the green compact subjected to the step (b) and to overlap at least a part of an edge portion of the unfired wiring insulating layer; a stacking step of stacking the plurality of green compacts including the green compact subjected to steps (a) to (c) to form a multi-layered body in which the unfired electrode lead is sandwiched between green compacts; a cutting step for cutting out an unfired sensor element from the multilayer body; and a firing step of firing the unfired sensor element to produce a sensor element including an electrode formed from the unfired electrode, an electrode lead formed from the unfired electrode lead, a lead insulating layer formed from the unfired lead insulating layer, and a bonding layer formed from the unfired bonding layer. [2] A manufacturing method for a sensor element according to claim 1, wherein in step (c), the unfired bonding layer is formed so that a maximum value Womax of a width of an overlapping portion of the unfired wiring insulating layer and the unfired bonding layer is 20 to 140 µm. [3] A manufacturing method for a sensor element according to claim 1 or 2, wherein in step (c), the unfired bonding layer is formed such that a ratio Womax / Wi of a maximum value Womax [µm] of a width of an overlapping portion of the unfired wiring insulating layer and the unfired bonding layer to a width Wi [µm] of the unfired wiring insulating layer in a direction perpendicular to a current flow direction of the unfired electrode line is 0.04 to 0.

29. [4] A manufacturing method for a sensor element according to any one of claims 1 to 3, wherein: the unfired wire insulating layer formed in step (b) includes a straight portion, the straight portion being arranged so that the unfired electrode does not lie on a line extending longitudinally from the straight portion; and in step (c), the unfired bonding layer is formed to overlap at least one edge portion of the straight portion positioned closer to the unfired electrode between the edge portions of the straight portion along the longitudinal direction. [5] A manufacturing method for a sensor element according to any one of claims 1 to 4, wherein: in step (a), an unfired measuring electrode, which is formed into a measuring electrode after firing, is formed as an unfired electrode; and in step (b), an unfired measuring electrode lead, which is connected to the unfired measuring electrode and is formed into a measuring electrode lead after firing, is formed as an unfired electrode lead. [6] A manufacturing method for a sensor element according to any one of claims 1 to 5, wherein: in steps (a) to (c), a plurality of patterns of each of the unfired electrode, the unfired electrode lead, the unfired lead insulating layer, and the unfired bonding layer are formed on the green compact such that the patterns, each pattern corresponding to a sensor element, are arranged in a predetermined direction perpendicular to a longitudinal direction of the sensor element; in the cutting step, a large number of the unfired sensor elements are cut out of the multilayer body; and in the firing step, the plurality of unfired sensor elements are fired to produce a plurality of sensor elements. [7] A manufacturing method for a sensor element according to claim 6, wherein: in step (b), the plurality of patterns of the unfired wiring insulation layer are formed such that the patterns, each pattern corresponding to a sensor element, are arranged in the predetermined direction at a first spacing distance; and in step (c), the plurality of patterns of the unfired bonding layer are formed such that the patterns, each pattern corresponding to a sensor element, are arranged in the predetermined direction in a second gap distance, the second gap distance being smaller than the first gap distance.

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