JP7126984B2 - Manufacturing method of sensor element, sensor element and gas sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a sensor element, a sensor element, and a gas sensor suitably used for detecting the gas concentration of a specific gas contained in combustion gas or exhaust gas of a combustor or an internal combustion engine, for example.

Conventionally, sensor elements have been used to detect the gas concentrations of ammonia and hydrocarbons in the exhaust gas of internal combustion engines. This sensor element has a solid electrolyte body, a reference electrode mainly composed of Pt and a detection electrode mainly composed of Au disposed on the solid electrolyte body, and is a mixed potential type element (Patent Reference 1).
Incidentally, since the melting point of Au in the sensing electrode is lower than the firing temperature of the element body including the solid electrolyte body and the reference electrode, it is difficult to simultaneously sinter the sensing electrode and the element body. After firing, the sensing electrode paste is printed on the element body, and the sensing electrode is fired at a low temperature.

JP 2017-90404 A

However, when the element body is fired, warping or bending occurs individually, and there is a problem that positional deviation is likely to occur when the paste for the detection electrode is printed on the surface. If the position of the detection electrode shifts, the characteristics (output, impedance, etc.) of the sensor change due to reasons such as a change in the distance from the reference electrode.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a sensor element, a sensor element, and a gas sensor that suppress positional displacement of a detection electrode formed later on an element body and suppress variation in sensor characteristics.

In order to solve the above problems, the method for manufacturing a sensor element of the present invention comprises: a solid electrolyte body; a reference electrode formed on the surface of the solid electrolyte body and containing Pt as a main component; In a method for manufacturing a sensor element having at least a detection electrode containing Au as a main component, an unfired alignment mark visible from the outside is formed on a green element main body provided with an unfired reference electrode and an unfired solid electrolyte body. an alignment mark forming step; an element body firing step of firing the unfired element body that has undergone the alignment mark forming step at a predetermined temperature; A green sensing electrode forming step of forming a sensing electrode on the surface of the solid electrolyte body, and a sensing electrode of firing the green sensing electrode at a temperature lower than the predetermined temperature after the green sensing electrode forming step. and a baking step.

According to this sensor element manufacturing method, after the solid electrolyte body and the reference electrode containing Pt as a main component are fired, the detection electrode containing Au as a main component is fired at a lower temperature. Au, which has a melting point lower than the temperature, is suppressed from sublimating when fired at a high temperature, and the detection electrode can be stably fired.
Unfired alignment marks are provided in advance on the element body before firing, and the formation positions of the unfired detection electrodes are positioned with reference to the alignment marks after firing, so that the element body after firing is warped or bent. However, since the alignment mark is also warped accordingly, the influence of the warp can be canceled, and the displacement of the detection electrode can be suppressed. As a result, it is possible to suppress fluctuations in the characteristics of the sensor (increase in output, impedance, etc.) due to changes in the positions of the detection electrode and the reference electrode.

In the alignment mark forming step, the green alignment mark may be formed so as to correspond to the position of the green reference electrode before being covered with the green solid electrolyte body.
According to this sensor element manufacturing method, since the unfired alignment mark is formed so as to correspond to the position of the unfired reference electrode, the unfired alignment mark can be accurately positioned with respect to the unfired reference electrode, which in turn can be detected. Positioning accuracy between the electrode and the reference electrode is further improved.

In the alignment mark forming step, the unfired reference electrode may be formed together with the unfired alignment mark, and the unfired alignment mark and the unfired reference electrode may be formed using a paste having the same composition. good.
According to this sensor element manufacturing method, the unfired alignment mark and the unfired reference electrode are formed together with paste having the same composition, thereby improving productivity.

In the alignment mark forming step, the unfired alignment marks may be formed so as to correspond to positions of unfired sensing leads formed on the surface of the unfired element body and connected to the unfired sensing electrodes. .
According to this sensor element manufacturing method, since the green alignment marks are formed so as to correspond to the positions of the green detection leads, the green alignment marks can be accurately positioned with respect to the green detection leads. It is possible to suppress misalignment with the detection electrode electrically connected to the firing detection lead, thereby suppressing electrical disconnection between the two.

In the alignment mark forming step, the unburned detection leads may be formed together with the unburned alignment marks, and the unburned alignment marks and the unburned detection leads may be formed using a paste having the same composition. good.
According to this sensor element manufacturing method, since the unfired alignment marks and the unfired detection leads are formed together with the paste having the same composition, the productivity is improved.

In the alignment mark forming step, the green alignment marks may be formed on both sides of the green reference electrode in the longitudinal direction of the green element body.
According to this sensor element manufacturing method, the detection electrodes are positioned using the two alignment marks on the element body that is elongated in the longitudinal direction. Therefore, even if the element body is shaken, the positioning is more accurate.

In the alignment mark forming step, a mark protection layer may be formed on the surface of the unfired alignment mark so that the fired alignment mark can be seen through.
According to this sensor element manufacturing method, it is possible to prevent the alignment mark from becoming unclear due to sublimation or the like of the components of the alignment mark during firing.

The sensor element of the present invention comprises a solid electrolyte body, a reference electrode formed on the surface of the solid electrolyte body and containing Pt as a main component, and a detection electrode formed on the surface of the solid electrolyte body and containing Au as a main component. The sensor element has at least an alignment mark formed on the sensor element, the alignment mark being visible from the outside and made mainly of a material having a melting point higher than that of Au.
According to this sensor element, by positioning the detection electrode with respect to the reference electrode based on the alignment marks at the time of manufacturing, fluctuations in sensor characteristics (output, impedance, etc.) due to changes in the positions of the detection electrode and the reference electrode, etc. ) can be suppressed.

A gas sensor according to the present invention includes a sensor element and a metal shell for holding the sensor element, and the sensor element according to claim 8 is used as the sensor element.

According to the present invention, it is possible to obtain a sensor element that suppresses positional displacement of a detection electrode formed later on the element body and suppresses variations in sensor characteristics.

1 is a cross-sectional view along the axial direction of a multi-gas sensor according to an embodiment of the present invention; FIG. 1 is a block diagram showing configurations of a multi-gas sensor and a gas sensor control device; FIG. It is a perspective view of a multi-sensor element part. FIG. 4 is a cross-sectional view in the width direction of the first ammonia sensor section and the second ammonia sensor section along line AA in FIG. 3; 4 is an exploded perspective view of a first ammonia sensor section and a second ammonia sensor section; FIG. FIG. 11 is a top view showing a mark protection layer covering alignment marks; 4A to 4C are process diagrams showing a method for manufacturing the multi-sensor element unit according to the first embodiment; FIG. 4 is a perspective view showing the structure of a laminate immediately before the step of firing the element body; FIG. 10 is a diagram showing an aspect of forming an unfired sensing electrode on the surface of a solid electrolyte body based on alignment marks in the unfired sensing electrode forming step; It is process drawing which shows the manufacturing method of the multi-sensor element part which concerns on 2nd Embodiment.

A multi-gas sensor and a multi-sensor element unit according to embodiments of the present invention will be described below with reference to FIGS. 1 to 6. FIG. 1 is a cross-sectional view along the direction of the axis O (longitudinal direction) of the multigas sensor, FIG. 2 is a block diagram for explaining the configuration of the multigas sensor device, FIG. 3 is a perspective view of the multisensor element part, and FIG. Cross-sectional view of the first ammonia sensor section and the second ammonia sensor section in the width direction along line AA, FIG. 5 is an exploded perspective view of the first ammonia sensor section and the second ammonia sensor section, and FIG. FIG. 4 is a top view showing a covering mark protection layer;

A multi-gas sensor (sensor) 200A of the present embodiment is used in a urea SCR system that purifies nitrogen oxides (NOx) contained in exhaust gas (gas to be measured) discharged from a diesel engine. More specifically, the concentrations of nitrogen monoxide (NO), nitrogen dioxide (NO ₂ ), and ammonia contained in the exhaust gas after reaction between NOx contained in the exhaust gas and ammonia (urea) are measured. It is.
The engine to which the multi-gas sensor 200A of the present embodiment is applied may be the diesel engine described above, or it may be applied to a gasoline engine, and the type of engine is not particularly limited.

As shown in FIG. 1, the multi-gas sensor 200A is an assembly in which a multi-sensor element section (sensor element) 100A for detecting ammonia concentration and NOx concentration is assembled. The multi-gas sensor 200A includes a plate-shaped multi-sensor element portion 100A extending in the axial direction, a tubular metal shell 138 having a screw portion 139 formed on its outer surface for fixing to an exhaust pipe, and the multi-sensor element portion 100A. A tubular ceramic sleeve 106 arranged so as to surround the periphery in the radial direction of the multi-sensor element portion 100A and an inner wall surface of a contact insertion hole 168 penetrating in the axial direction are arranged in a state surrounding the rear end portion of the multi-sensor element portion 100A. A first insulating contact portion 166 and a plurality of terminal fittings 110 (only two are shown in FIG. 1) arranged between the multi-sensor element portion 100A and the insulating contact portion 166 are provided. The terminal fitting 110 has a front end side terminal fitting 111 and a rear end side terminal fitting 112, and the contacts of both the terminal fittings 111 and 112 are positioned at the front end side and the rear end side in the axis O direction.
The multi-gas sensor 200A and the multi-sensor element unit 100A correspond to the "sensor" and "sensor element" in the claims, respectively.

The metallic shell 138 has a through hole 154 penetrating in the direction of the axis O, and has a substantially cylindrical shape with a shelf portion 152 protruding radially inward of the through hole 154 . In addition, the metal shell 138 is arranged such that the front end side of the multi-sensor element portion 100A is arranged outside the front end side of the through hole 154, and the plurality of electrode pads 80 (see FIG. 4) are arranged outside the rear end side of the through hole 154. , the multi-sensor element section 100A is held in the through hole 154. As shown in FIG. Further, the shelf portion 152 is formed as an inwardly tapered surface that is inclined with respect to a plane perpendicular to the axial direction.
For the sake of simplification, the electrode pads on the front and back surfaces of the multi-sensor element section 100A are represented by reference numeral 80 in FIG. A plurality of electrodes are formed according to the number of electrodes, etc., possessed by the .

Inside the through-hole 154 of the metal shell 138, there are provided an annular ceramic holder 151, a powder-filled layer 153 (hereinafter also referred to as a talc ring 153), and the above-mentioned ceramic sleeves 106 are laminated in this order from the front end side to the rear end side. A crimping packing 157 is arranged between the ceramic sleeve 106 and the rear end portion 140 of the metal shell 138 , and a talc ring 153 is arranged between the ceramic holder 151 and the shelf portion 152 of the metal shell 138 . and a metal holder (not shown) for holding the ceramic holder 151 is arranged. The rear end portion 140 of the metallic shell 138 is caulked through a caulking packing 157 so as to press the ceramic sleeve 106 toward the distal end side.

On the other hand, on the outer periphery of the front end side (lower side in FIG. 1) of the metal shell 138, a double external protector 142 made of metal (for example, stainless steel) having a plurality of holes and covering the projecting portion of the multi-sensor element section 100A is provided. and an internal protector 143 are attached by welding or the like.

An outer cylinder 144 is fixed to the rear end side outer circumference of the metallic shell 138 . In addition, in the opening on the rear end side (upper side in FIG. 1) of the outer cylinder 144, there are a plurality of lead wires 146 (four in FIG. 1) electrically connected to the electrode pads 80 of the multi-sensor element section 100A. A grommet 150 formed with a lead wire insertion hole 161 through which a wire is inserted, and a second insulating contact portion 170 are arranged in this order from the rear end side.

A first insulating contact portion 166 is in contact with the tip of a second insulating contact portion 170 on the rear end side (upper side in FIG. 1) of the multi-sensor element portion 100A projecting from the rear end portion 140 of the metal shell 138. placed. The first insulating contact portion 166 is arranged around the electrode pads 80 formed on the front and back surfaces on the rear end side of the multi-sensor element portion 100A. The first insulating contact portion 166 is formed in a cylindrical shape having a contact insertion hole 168 extending axially therethrough, and is provided with a flange portion 167 protruding radially outward from the outer surface. The first insulating contact portion 166 is arranged inside the outer cylinder 144 by the collar portion 167 coming into contact with the outer cylinder 144 via the holding member 169 . The terminal metal fitting 110 on the first insulating contact portion 166 side and the electrode pad 80 of the multi-sensor element portion 100A are electrically connected, and the lead wire 146 conducts with the outside.

As shown in FIG. 2, the multi-sensor element section 100A includes a NO _x sensor section 30A having a configuration similar to that of a known NO _x sensor, and two ammonia sensor sections, a first ammonia sensor section 42x and a second ammonia sensor section. The first ammonia sensor portion 42x and the second ammonia sensor portion 42y are formed on the outer surface of the _NOx sensor portion 30A, as described later in detail.

First, the NO _x sensor section 30A includes an insulating layer 23e, a first solid electrolyte body 2a, an insulating layer 23d, a third solid electrolyte body 6a, an insulating layer 23c, a second solid electrolyte body 4a, and insulating layers 23b and 23a. It has a structure laminated in order. A first measurement chamber S1 is defined between the layers of the first solid electrolyte body 2a and the third solid electrolyte body 6a. Exhaust gas is introduced from outside. A porous protective layer 9 is arranged outside the first diffusion resistor 8a.
A second diffusion resistor 8b is disposed at the end of the first measurement chamber S1 opposite to the entrance, and the right side of the first measurement chamber S1 communicates with the first measurement chamber S1 via the second diffusion resistor 8b. A second measuring chamber S2 is defined. The second measurement chamber S2 penetrates the third solid electrolyte body 6a and is formed between the first solid electrolyte body 2a and the second solid electrolyte body 4a.

A long plate-shaped heating resistor 21 extending along the direction of the axis O of the multi-sensor element section 100A is embedded between the insulating layers 23b and 23a. The heat-generating resistor 21 has a heat-generating portion on the front end side in the direction of the axis O, and a pair of lead portions extending from the heat-generating portion toward the rear end side in the axial direction. This heater is used to raise the temperature of the gas sensor to an activation temperature, increase the oxygen ion conductivity of the solid electrolyte body, and stabilize the operation.

The first pumping cell 2 includes a first solid electrolyte body 2a mainly made of zirconia having oxygen ion conductivity, an inner first pumping electrode 2b disposed so as to sandwich the solid electrolyte body 2a, and an outer first pumping electrode serving as a counter electrode. 2c, the inner first pumping electrode 2b facing the first measuring chamber S1. Both the inner first pumping electrode 2b and the outer first pumping electrode 2c are mainly made of platinum, and the surface of the inner first pumping electrode 2b is covered with a protective layer 11 made of a porous material.
Further, the insulating layer 23e corresponding to the upper surface of the outer first pumping electrode 2c is hollowed out and filled with the porous material 13 so that the outer first pumping electrode 2c and the outside are communicated to allow gas (oxygen) to flow in and out. there is

The oxygen concentration detection cell 6 includes a third solid electrolyte body 6a mainly made of zirconia, and a detection electrode 6b and a reference electrode 6c sandwiching the third solid electrolyte body 6a. The detection electrode 6b is the inner first pumping electrode 2b. It faces the first measurement chamber S1 on the further downstream side. Both the detection electrode 6b and the reference electrode 6c are mainly made of platinum.
The insulating layer 23c is cut out so that the reference electrode 6c in contact with the third solid electrolyte body 6a is arranged therein, and the cutout portion is filled with a porous material to form the reference oxygen chamber 15. . Then, by applying a weak constant current to the oxygen concentration detection cell 6 using the Icp supply circuit 54 in advance, oxygen is sent from the first measurement chamber S1 into the reference oxygen chamber 15 to be used as the oxygen reference.

The second pumping cell 4 includes a second solid electrolyte body 4a mainly made of zirconia, an inner second pumping electrode 4b and a counter electrode arranged on the surface of the second solid electrolyte body 4a facing the second measurement chamber S2. and a second pumping counter electrode 4c. Both the inner second pumping electrode 4b and the second pumping counter electrode 4c are based on platinum.
The second pumping counter electrode 4c is arranged in a cutout portion of the insulating layer 23c on the second solid electrolyte body 4a and faces the reference oxygen chamber 15 so as to face the reference electrode 6c.
The inner first pumping electrode 2b, the detection electrode 6b, and the inner second pumping electrode 4b are each connected to a reference potential.

Next, the first ammonia sensor section 42x and the second ammonia sensor section 42y, which are two ammonia sensor sections (cells), will be described.
As shown in FIG. 3, the multi-sensor element section 100A has a first ammonia sensor section 42x and a second ammonia sensor section 42y that are spaced apart in the width direction. 3 shows the multi-sensor element section 100A of FIG. 2 turned upside down.

The first ammonia sensor section 42x and the second ammonia sensor section 42y are formed on the insulating layer 23a forming the outer surface (lower surface) of the NO _x sensor section 30A. More specifically, as shown in FIGS. 4 and 5, a common reference electrode 42a is formed on the insulating layer 23a, and a narrow common solid electrolyte body 42d is formed in the center of the surface of the common reference electrode 42a in the width direction. there is Further, a reference electrode insulating layer 42c is formed on both widthwise side surfaces of the common reference electrode 42a where the common solid electrolyte body 42d is not formed.
A first detection electrode 42bx is formed on the surface of the common solid electrolyte body 42d to reach the reference electrode insulating layer 42c on one end side in the width direction. The first ammonia sensor section 42x detects the concentration of ammonia in the gas to be measured based on the change in electromotive force between the common reference electrode 42a and the first detection electrode 42bx.
Similarly, a second detection electrode 42by is formed on the surface of the common solid electrolyte body 42d to reach the reference electrode insulating layer 42c on the other end side in the width direction. Then, the second ammonia sensor section 42y detects the concentration of ammonia in the gas to be measured based on the change in electromotive force between the common reference electrode 42a and the second detection electrode 42by.

The first detection electrode 42bx and the second detection electrode 42by can be made of a material containing Au as a main component (more than at least 50% by mass, for example 70% by mass or more) and containing Pt or Pd. The common reference electrode 42a can be made of Pt alone or a material containing Pt as a main component (at least more than 50 mass %, for example, 70 mass % or more).
The first detection electrode 42bx and the second detection electrode 42by are electrodes in which ammonia gas is difficult to burn on the electrode surface. On the other hand, since the common reference electrode 42a readily burns ammonia gas on the electrode surface, each electrode detects the concentration of ammonia in a mixed potential manner. Ammonia reacts (electrode reaction) with oxygen ions at the three-phase interface described below, and the concentration of ammonia can be detected.
The common solid electrolyte body 42d is made of, for example, partially stabilized zirconia (YSZ).
Also, the first ammonia sensor section 42x and the second ammonia sensor section 42y may be covered with a porous protective layer.

The common reference electrode 42a and the common solid electrolyte body 42d correspond to the "reference electrode" and the "solid electrolyte body" in the claims, respectively.
Also, the first detection electrode 42bx and the second detection electrode 42by respectively correspond to the "detection electrode" in the claims.

Next, returning to FIG. 2, an example of the configuration of the control device 300 will be described. The control device 300 includes an (analog) control circuit 59 and a microcomputer 60 on a circuit board.
A microcomputer 60 controls the entire control device 300 and includes a CPU (Central Processing Unit) 61, a RAM 62, a ROM 63, a signal input/output unit 64, an A/D converter 65, and a clock (not shown). The program is executed by the CPU. Control device 300 exchanges signals with ECU 220 via signal input/output unit 64 .
A gas sensor unit 400 is configured by combining the multi-sensor element section 100A (multi-gas sensor 200A) and the control device 300 .

The control circuit 59 includes a reference voltage comparison circuit 51, an Ip1 drive circuit 52, a Vs detection circuit 53, an Icp supply circuit 54, an Ip2 detection circuit 55, a Vp2 application circuit 56, a heater drive circuit 57, and a first ammonia sensor. A first electromotive force detection circuit 58a and a second electromotive force detection circuit 58b are provided for detecting the electromotive forces of the section 42x and the second ammonia sensor section 42y.
The control circuit 59 controls the NO _x sensor section 30A, detects the first pumping current Ip1 and the second pumping current Ip2 flowing through the NO _x sensor section 30A, and outputs them to the microcomputer 60. FIG.
The first electromotive force detection circuit 58a and the second electromotive force detection circuit 58b detect the ammonia concentration output (electromotive force) between the electrodes of the first ammonia sensor section 42x and the second ammonia sensor section 42y, and the microcomputer 60 Output.

Specifically, the outer first pumping electrode 2c of the _NOx sensor section 30A is connected to the Ip1 drive circuit 52, and the reference electrode 6c is connected to the Vs detection circuit 53 and the Icp supply circuit 54 in parallel. The second pumping counter electrode 4c is connected in parallel to an Ip2 detection circuit 55 and a Vp2 application circuit 56. FIG. The heater circuit 57 is connected to a heater (specifically, the heating resistor 21).
A pair of electrodes 42ax and 42bx of the first ammonia sensor section 42x are each connected to the first electromotive force detection circuit 58a. Similarly, a pair of electrodes 42ay and 42by of the second ammonia sensor section 42y are connected to the second electromotive force detection circuit 58b.

Each of the circuits 51-57 has the following functions.
The Ip1 drive circuit 52 detects the first pumping current Ip1 while supplying the first pumping current Ip1 between the inner first pumping electrode 2b and the outer first pumping electrode 2c.
The Vs detection circuit 53 detects the voltage Vs between the detection electrode 6b and the reference electrode 6c, and outputs the detection result to the reference voltage comparison circuit 51. FIG.
The reference voltage comparison circuit 51 compares the reference voltage (eg, 425 mV) with the output (voltage Vs) of the Vs detection circuit 53 and outputs the comparison result to the Ip1 drive circuit 52 . The Ip1 drive circuit 52 controls the direction and magnitude of the Ip1 current so that the voltage Vs becomes equal to the reference voltage, and the oxygen concentration in the first measurement chamber S1 is set to a predetermined value that does not decompose _NOx . adjust to
The Icp supply circuit 54 sends a weak current Icp between the detection electrode 6b and the reference electrode 6c to send oxygen from the first measurement chamber S1 into the reference oxygen chamber 15, and the reference electrode 6c reaches a predetermined oxygen concentration as a reference. expose to
The Vp2 applying circuit 56 applies a constant voltage Vp2 (for example, 450 mV) between the inner second pumping electrode 4b and the second pumping counter electrode 4c to such an extent that the _NOx gas in the gas under test is decomposed into oxygen and _N2 gas. is applied to decompose the _NOx into nitrogen and oxygen.

The Ip2 detection circuit 55 controls the second pumping cell 4 when the oxygen generated by decomposition of _NOx is pumped from the second measurement chamber S2 through the second solid electrolyte body 4a to the second pumping counter electrode 4c side. A flowing second pumping current Ip2 is detected.
At this time, since there is a linear relationship between the second pumping current _Ip2 and the NOx concentration, the Ip2 detection circuit 55 detects the second pumping current Ip2, thereby detecting the _NOx concentration in the measured gas. can be done.

The first electromotive force detection circuit 58a detects the ammonia concentration output (electromotive force) between the pair of electrodes 42ax and 42bx, and the second electromotive force detection circuit 58b detects the ammonia concentration output (electromotive force) between the pair of electrodes 42ay and 42by. By detecting the electric power), the concentration of ammonia in the gas to be measured can be detected as described later.
The reason why the two ammonia sensor units, the first ammonia sensor unit 42x and the second ammonia sensor unit 42y, are provided is as follows. That is, the ammonia sensor section detects not only ammonia but also NO ₂ , so if the gas to be detected contains NO ₂ gas other than ammonia, the detection accuracy of ammonia decreases. Therefore, if two ammonia sensor units with different ratios of sensitivity to ammonia and sensitivity to NOx are provided, values based on different sensitivities will be obtained from the two ammonia sensor units for _two unknown concentrations of ammonia gas and NO2 gas. Since it is detected, the concentrations of ammonia gas and NO ₂ can be calculated.

Next, features of the multi-sensor element unit 100A according to the embodiment of the present invention will be described with reference to FIGS. 3, 5, and 6. FIG. As shown in FIG. 3, alignment marks M1 and M2 visible from the outside are formed on the side of the ammonia sensor section of the multi-sensor element section 100A.
5 and 6, in this embodiment, alignment marks M1 and M2 are formed on the ammonia sensor side of the multi-sensor element portion 100A, and the surfaces of the alignment marks M1 and M2 are covered with mark protection. Layers 42M1 and 42M2 are coated so that alignment marks M1 and M2 are visible through mark protection layers 42M1 and 42M2.

The alignment marks M1 and M2 being "visible from the outside" means that the alignment marks M1 and M2 are covered with the mark protection layers 42M1 and 42M2 as shown in FIG. It includes both cases where it is exposed on the surface of 100A. If the mark protection layers 42M1 and 42M2 are, for example, insulating ceramic thin layers, the alignment marks M1 and M2 can be seen through the mark protection layers 42M1 and 42M2.

Further, as described in the manufacturing method described later, it is preferable that the alignment marks M1 and M2 are mainly composed of a material having a melting point higher than that of Au (exceeding 50% by mass). If the alignment marks M1 and M2 are mainly composed of a material having a melting point or lower than that of Au, the alignment marks may not be melted depending on the firing temperature when the sensing electrodes mainly composed of Au are fired in the sensing electrode firing process. This is because M1 and M2 may melt and become unable to maintain their shape.
Materials having a higher melting point than Au include Pt, Pd, Rh, and alloys thereof.
In addition, when the mark protection layers 42M1 and 42M2 are provided, it is possible to prevent the components of the alignment marks M1 and M2 from sublimating and making the marks unclear during the above-described firing.

Next, a method for manufacturing the multi-sensor element section 100A according to the embodiment of the present invention will be described.
First, a method for manufacturing the multi-sensor element section 100A according to the first embodiment will be described with reference to FIGS. 7 to 9. FIG.
As shown in FIG. 7A, first, an unfired reference electrode lead U42aL and unfired detection lead bases U42bL1 and U42bL2 are formed on the surface of an unfired element body U30A by paste printing or the like. Note that "U" in the note head of each member below represents unfired, and corresponds to the reference numeral of each member after firing in FIG. Further, in this embodiment, the unfired element main body U30A is the unfired NO _x sensor section 30A.
The unfired reference electrode lead U42aL has a bifurcated shape on the tip side, and the unfired detection lead bases U42bL1 and U42bL2 linearly extend in the axis O direction. The unfired detection lead bases U42bL1 and U42bL2 are formed so as to sandwich the rear end side of the unfired reference electrode lead U42aL from both sides.

Next, as shown in FIG. 7B, rectangular unfired alignment marks UM1 and UM2 and an unfired common reference electrode U42a are formed together by paste printing or the like (alignment mark forming step). If the unfired alignment marks UM1 and UM2 and the unfired common reference electrode U42a are formed together with paste having the same composition, productivity is improved.
The unfired common reference electrode U42a has a U-shape, and the U-shape faces the rear end side. Then, unfired alignment marks UM1 and UM2 are formed in front and rear of the unfired element main body U30A in the longitudinal direction (direction of the axis O), respectively, with the unfired common reference electrode U42a interposed therebetween.
Each rear end side of the U-shaped unfired common reference electrode U42a is overlapped with the tip end of the bifurcated unfired reference electrode lead U42aL.

Next, as shown in FIG. 7C, an unfired common solid electrolyte body U42d is formed by paste printing or the like so as to partially cover the unfired common reference electrode U42a. A rectangular unfired common solid electrolyte body U42d is formed so as to cover the central portion in the width direction of the unfired common reference electrode U42a.
Next, as shown in FIG. 7(d), on both sides of the unfired common reference electrode U42a where the unfired common solid electrolyte bodies U42d are not formed, rectangular unfired reference electrode insulating layers elongated in the longitudinal direction are formed. U42c is formed by paste printing or the like.
Further, each unfired reference electrode insulating layer U42c covers an unfired reference electrode lead U42aL whose tip is bifurcated.

Next, as shown in FIG. 7(e), unfired detection lead tip portions U42bxL and U42byL are formed on the surface of the unfired reference electrode insulating layer U42c by paste printing or the like.
Each unfired detection lead tip portion U42bxL, U42byL is overlapped with an unfired reference electrode lead U42aL bifurcated with an unfired reference electrode insulating layer U42c interposed therebetween, and is insulated by the unfired reference electrode insulating layer U42c. Also, the rear ends of the unfired detection lead tip portions U42bxL and U42byL overlap the tips of the unfired detection lead base portions U42bL1 and U42bL2.

Further, as shown in FIG. 7(f), a substantially rectangular unfired second insulating layer U42f with a U-shaped portion facing the tip side is formed by paste printing or the like.
The non-fired second insulating layer U42f consists of the rear end side of the non-fired reference electrode lead U42aL (one linear portion where the two-forked branches gather), the non-fired detection lead bases U42bL1 and U42bL2, and the non-fired detection lead tip portions. U42bxL, U42byL cover the unfired reference electrode insulating layer U42c (see FIG. 8).

On the other hand, unfired alignment marks UM2 (unfired mark protection layers U42M2 to be described later) are exposed from the U-shaped openings 42s of the unfired second insulating layers U42f.
Further, on the tip side from the tip of the unfired second insulating layer U42f, an unfired common solid electrolyte body U42d, an unfired alignment mark UM1 (an unfired mark protection layer U42M1 to be described later), unfired detection lead tip portions U42bxL and U42byL. And the tip side of the unfired reference electrode insulating layer U42c is exposed (see FIG. 8).
On the other hand, the unfired detection lead bases U42bL1 and U42bL2 and the unfired reference electrode lead U42aL are exposed on the rear end side from the rear end of the unfired second insulating layer U42f. Each lead exposed at the rear end of the unfired second insulating layer U42f functions as an electrode pad and is electrically connected to a terminal fitting (not shown), which is connected to a lead wire. .

Further, as shown in FIG. 7(f), along with the unfired second insulating layer U42f, unfired mark protection layers U42M1 and U42M2, each having a rectangular shape slightly larger than the unfired alignment marks UM1 and UM2, are unfired. It is formed by paste printing or the like so as to cover the alignment marks UM1 and UM2. It is preferable to form the unfired mark protection layers U42M1 and U42M2 and the unfired second insulating layer U42f together with a paste having the same composition, because this improves productivity.

Then, as shown in FIG. 9, the unfired laminate thus obtained is fired at a predetermined temperature (element body firing step).
Next, based on the alignment marks M1 and M2 in FIG. 9, the unfired detection electrodes U42bx and U42by are formed on the surfaces of the common solid electrolyte body U42d and the detection lead tips 42bxL and U42byL by paste printing or the like (unfired detection electrodes forming process). Subsequently, the unfired sensing electrodes U42bx and U42by are fired at a temperature lower than the predetermined temperature used in the element body firing step (sensing electrode firing step). The firing temperature is desirably less than 1064° C. (for example, 1000° C.), which is the melting point of Au at normal pressure.
In this way, the ammonia sensor section of FIG. 5 corresponding to FIGS. 7 and 9 is completed. 5 corresponds to the reference numerals in FIGS. 7 and 9 excluding "U" indicating unburned.

As described above, after the common solid electrolyte body 42d and the common reference electrode 42a mainly composed of Pt are fired, the detection electrodes 42bx and 42by mainly composed of Au are fired at a lower temperature than the common solid electrolyte body 42d. Au, which has a lower melting point than the firing temperature of the electrode 42a, is suppressed from sublimating due to firing at a high temperature, and the detection electrodes 42bx and 42by can be stably fired.
Unfired alignment marks UM1 and UM2 are provided in advance on the element main body 30A before firing. Even if the element main body 30A is warped or bent later, the alignment marks M1 and M2 are also warped accordingly, so that the influence of the warp can be canceled and the displacement of the detection electrodes 42bx and 42by can be suppressed. As a result, it is possible to suppress fluctuations in sensor characteristics (increase in impedance, etc.) due to changes in the positions of the detection electrodes 42bx, 42by and the common reference electrode 42a.

In the first embodiment, the unfired alignment marks UM1 and UM2 are formed so as to correspond to the positions of the unfired common reference electrode U42a before being covered with the unfired common solid electrolyte body U42d. The unburned alignment marks UM1 and UM2 can be accurately positioned with respect to the common reference electrode U42a, and the positioning accuracy between the detection electrodes 42bx and 42by and the reference electrode 42a is further improved.
In addition, since the unfired alignment marks UM1 and UM2 are formed before the unfired common solid electrolyte body U42d is arranged on the surface of the unfired common reference electrode U42a, the unfired common reference electrode U42a becomes invisible and the unfired detection is impossible. Difficulty in positioning the electrodes U42bx and U42by can be suppressed.
Here, "correspondingly" includes the case where the unfired alignment marks UM1 and UM2 are formed according to the position of the unfired common reference electrode U42a without detecting the position of the unfired common reference electrode U42a. For example, as described above, the unfired common reference electrode U42a and the unfired alignment marks UM1 and UM2 are formed at once using the same printing mask.
Further, "correspondingly" means that only the unfired common reference electrode U42a is formed in advance, the position of the unfired common reference electrode U42a is detected, and the unfired alignment marks UM1 and UM2 are formed according to the detected position. is formed later.

In the first embodiment, unfired alignment marks UM1 and UM2 are formed on the front and rear sides of the unfired common reference electrode U42a in the longitudinal direction (axis O direction) of the unfired element body U30A.
As a result, the detection electrodes 42bx and 42by are positioned using the two alignment marks M1 and M2 on the element body that is elongated in the longitudinal direction, so even if the element body is shaken, the positioning is more accurate.

Next, a method for manufacturing the multi-sensor element section 100A according to the second embodiment will be described with reference to FIG.
The method of manufacturing the multi-sensor element unit 100A according to the second embodiment is the same as that of the first embodiment except that the formation positions and formation order of the unfired alignment marks UM11 and UM12 are different from those of the first embodiment. Therefore, in FIG. 10 corresponding to FIG. 7, only step (e) is different, and FIGS. 8 and 9 are the same as the first embodiment.
That is, as shown in FIG. 10, in the second embodiment, the green alignment marks UM11 and UM12 are not formed in the step (b), and the green alignment marks UM11 and UM12 are formed in the step (e). Unfired detection lead tip portions U42bxL and U42byL are formed together by paste printing or the like (alignment mark forming step).
Subsequent step (f) and subsequent steps are the same as in the first embodiment.

Also in the second embodiment, Au, which has a lower melting point than the firing temperature of the common reference electrode 42a, is suppressed from sublimating due to firing at a high temperature, and the detection electrodes 42bx and 42by can be stably fired.
Further, since the formation positions of the unfired detection electrodes U42bx and U42by are positioned with reference to the alignment marks in the fired element main body 30A, positional deviation of the detection electrodes 42bx and 42by can be suppressed. As a result, it is possible to suppress fluctuations in sensor characteristics due to changes in the positions of the detection electrodes 42bx, 42by and the common reference electrode 42a.

Furthermore, in the second embodiment, unfired alignment marks UM11 and UM12 are formed so as to correspond to the positions of unfired sensing lead tip portions U42bxL and U42byL connected to unfired sensing electrodes U42bx and U42by. .
As a result, the unfired detection lead tips U42bxL and U42byL are positioned by the unfired alignment marks UM11 and UM12, thereby suppressing the positional deviation between the unfired detection electrodes U42bx and U42by and the unfired detection lead tips U42bxL and U42byL. can be suppressed from being electrically disconnected.
The meaning of "correspondingly" is the same as described above.

It goes without saying that the present invention is not limited to the above-described embodiments, but extends to various modifications and equivalents within the spirit and scope of the present invention.
For example, the reference electrode and the detection electrode may be formed in parallel on the same surface of the solid electrolyte body. In this case, after forming the unfired reference electrode and the alignment mark on the surface of the solid electrolyte body included in the unfired element body, firing is performed (element body firing step), then the unfired detection electrode is formed and fired at a low temperature. (detection electrode firing step).
In this case as well, the alignment marks can be used to accurately determine the positions of the reference electrode and the detection electrode on the same surface of the solid electrolyte body.
Alternatively, for example, alignment marks and an ammonia sensor may be formed on a ceramic green sheet separate from the NOx sensor by the same means as in the above embodiment, and joined to the baked NOx sensor. In this case, the ceramic green sheet corresponds to the "unfired element body", and the fired ceramic sheet corresponds to the "element body".

Also, the shape, number, and position of the alignment marks are not limited as long as they can be visually recognized from the outside.
In the above-described embodiment, one reference electrode and one solid electrolyte body are provided in common for two detection electrodes. good too.
Furthermore, in the above embodiment, the multi-sensor element unit is used, but the present invention is not limited to this, and the ammonia sensor unit may be a single ammonia sensor element or a sensor having the same configuration as the ammonia sensor unit and capable of detecting hydrocarbons. It may be various sensor elements such as elements.

30A element body 42a reference electrode (common reference electrode)
42bx, 42by detection electrode 42d solid electrolyte 42M1, 42M2 mark protective layer M1, M2, M11, M12 alignment mark U30A unfired element body U42a unfired reference electrode (common reference electrode)
U42bx, U42by Unsintered detection electrode U42d Unsintered solid electrolyte body U42bxL, U42byL Unsintered detection lead (tip of unsintered detection lead)
UM1, UM2, UM11, UM12 unburned alignment mark 100A sensor element (multi-sensor element part)
138 metal shell 200A gas sensor (multi-gas sensor)

Claims (9)

A method for manufacturing a sensor element having at least a solid electrolyte body, a reference electrode formed on the surface of the solid electrolyte body and containing Pt as a main component, and a detection electrode formed on the surface of the solid electrolyte body and containing Au as a main component. in
an alignment mark forming step of forming an unfired alignment mark visible from the outside on the unfired element body provided with the unfired reference electrode and the unfired solid electrolyte body;
an element body firing step of firing at a predetermined temperature the unfired element body that has undergone the alignment mark forming step;
an unfired detection electrode forming step of forming an unfired detection electrode on the surface of the solid electrolyte body based on the alignment mark after the element body firing step;
a sensing electrode firing step of firing the unfired sensing electrode at a temperature lower than the predetermined temperature after the unfired sensing electrode forming step;
A method for manufacturing a sensor element, comprising: 2. The method according to claim 1, wherein in said alignment mark forming step, said unfired alignment mark is formed so as to correspond to a position of said unfired reference electrode before being covered with said unfired solid electrolyte body. A method for manufacturing a sensor element. In the alignment mark forming step, the unfired reference electrode is also formed together with the unfired alignment mark, and the unfired alignment mark and the unfired reference electrode are formed using a paste having the same composition. 3. A method for manufacturing a sensor element according to claim 2. In the alignment mark forming step, the green alignment mark is formed so as to correspond to the position of the green detection lead formed on the surface of the green element body and connected to the green detection electrode. The method for manufacturing a sensor element according to claim 1, wherein In the alignment mark forming step, the unburned detection leads are formed together with the unburned alignment marks, and the unburned alignment marks and the unburned detection leads are formed using a paste having the same composition. 5. A method for manufacturing a sensor element according to claim 4. 6. The alignment mark forming step, wherein the unfired alignment marks are formed on both sides of the unfired reference electrode in the longitudinal direction of the green element body. A method for manufacturing the sensor element according to 1. 7. The alignment mark forming step according to any one of claims 1 to 6, wherein a mark protection layer is formed on the surface of the unfired alignment mark so that the fired alignment mark can be seen through. A method for manufacturing a sensor element. a solid electrolyte body;
a reference electrode formed on the surface of the solid electrolyte body and containing Pt as a main component;
A sensor element having at least a detection electrode formed on the surface of the solid electrolyte body and containing Au as a main component,
A sensor element, wherein an alignment mark, which is visible from the outside and whose main component is a material having a melting point higher than that of Au, is formed on the sensor element. A gas sensor comprising a sensor element and a metal shell for holding the sensor element, wherein the sensor element according to claim 8 is used as the sensor element.

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