JP6586368B2 - Manufacturing method of sensor element, sensor element and gas sensor - Google Patents

Description

  The present invention relates to a method for manufacturing a sensor element, a sensor element, and a gas sensor.

  Conventionally, a gas sensor that detects the concentration of a predetermined gas such as NOx in a gas to be measured such as an exhaust gas of an automobile is known. In the sensor element of this gas sensor, a conductive electrode is formed in a through hole formed so as to penetrate the solid electrolyte layer and the inner peripheral surface is covered with an insulating layer, thereby conducting between the conductive portions on the front and back of the solid electrolyte layer. Is known. As a method of covering the inner peripheral surface of the through hole with the insulating layer, the insulating layer paste is screen printed on the surface of the unfired solid electrolyte sheet on which the through hole is formed, and the insulating layer paste flows down into the through hole. The method of making it known is known (for example, patent document 1). Such a method is also called through-hole printing. Further, the following methods are known as methods for forming a conductive electrode in a through hole. First, a metal mask having a through hole and a green sheet on which a through hole is formed are prepared, the through hole and the through hole are aligned, and both are fixed. Subsequently, the conductive paste supplied on the metal mask is filled into the through hole by moving the squeegee (for example, Patent Document 2).

Japanese Patent No. 4413362 JP 2011-159839 A

  By the way, when filling the through hole with the conductive paste after covering the inside of the through hole with the insulating layer paste, the insulating layer paste flows as the conductive paste moves through the through hole. was there. And when the insulating layer paste is poured, a part where the thickness of the insulating layer is insufficient is generated on a part of the inner peripheral surface of the through hole, and a part where the insulation of the conductor by the insulating layer is insufficient is generated. was there.

  The present invention has been made to solve such a problem, and a main object of the present invention is to prevent partial insulation of the conductor by the insulating layer in the through hole.

  The present invention employs the following means in order to achieve the main object described above.

The manufacturing method of the sensor element of the present invention includes:
(A) A green structure having a single green sheet or a plurality of stacked green sheets and having a first opening and a through hole having a second opening opposite to the first opening is prepared. Process,
(B) A step of forming an unsintered insulating layer by coating the inner peripheral surface of the through hole with an insulating paste, in a direction perpendicular to the central axis in a sectional view along the central axis of the through hole The first opening side from the center of the axial direction in the through hole as a first region, the second opening side as a second region, and the unsintered insulating layer in the first region When the shortest distance in the height direction from the central axis is a distance D1, and the shortest distance in the height direction between the green insulating layer in the second region and the central axis is a distance D2, the distance Performing the coating so that D1 <distance D2.
(C) after the step (b), filling the through hole with a conductive paste from the first opening side to form an unfired conductor;
(D) after the step (c), firing the green structure to obtain a sensor element having a structure in which the unsintered insulating layer becomes an insulating layer and the unsintered conductor becomes a conductor; ,
Is included.

  In this method of manufacturing the sensor element, the inner peripheral surface of the through hole is coated with an insulating paste to form a green insulating layer, and the coating is performed so that distance D1 <distance D2. That is, when the first opening side is the first region and the second opening side is the second region from the axial center in the through hole, the unsintered insulating layer in the first region is unsintered in the second region. The unsintered insulating layer is formed so as to have a raised portion that swells radially inward of the through hole as compared with the insulating layer. Thereafter, a conductive paste is filled into the through hole from the first opening side to form an unfired conductor. Here, when the conductive paste is filled from the first opening side, the unfired insulating layer in the first region is more likely to flow toward the second opening side with the movement of the conductive paste than in the second region. However, in the method for manufacturing a sensor element of the present invention, the unfired insulating layer in the first region has a raised portion in advance in consideration of the amount that flows to the second opening side. As a result, the boundary between the insulating layer and the conductor after the filling and firing of the conductive paste becomes a relatively flat shape as compared with the case where such a raised portion is not formed in advance. Therefore, it is difficult to generate a portion where the thickness of the insulating layer in the through hole is insufficient. Therefore, partial insulation of the conductor by the insulating layer in the through hole can be suppressed.

  In the method for manufacturing a sensor element of the present invention, in the step (b), a first treatment for flowing the insulating paste into the inner peripheral surface from the first opening side, and the insulating paste on the second opening side. And the second treatment that flows into the inner peripheral surface is performed once or more, and the insulating paste having a higher viscosity than the first treatment may be used in the second treatment. Here, when the first treatment is performed, the insulating paste tends to swell on the second region side, and when the second treatment is performed, the first region side tends to swell. Then, by using an insulating paste having a higher viscosity in the second process than in the first process, the height of the raised portion of the unfired insulating layer in the first region is likely to increase. Therefore, it is possible to relatively easily form an unsintered insulating layer satisfying the distance D1 <distance D2, and to suppress partial insulation of the conductor by the insulating layer in the through hole.

  In the method for manufacturing a sensor element of the present invention, in the step (b), the insulating paste is caused to flow from the first opening side to the inner peripheral surface while sucking the inside of the through hole from the second opening side. One treatment and a second treatment for causing the insulating paste to flow into the inner peripheral surface from the second opening side while sucking the inside of the through hole from the first opening side, respectively, and In the second process, the suction force may be weaker than that in the first process. Here, when the first treatment and the second treatment are performed, if the suction force is too strong, the amount of the insulating paste that passes through the through hole increases, and the height of the raised portion decreases. There is. Therefore, by reducing the suction force in the second process as compared with the first process, the height of the raised portion of the unfired insulating layer in the first region is likely to increase. Therefore, it is possible to relatively easily form an unsintered insulating layer satisfying the distance D1 <distance D2, and to suppress partial insulation of the conductor by the insulating layer in the through hole.

  In the method for manufacturing a sensor element of the present invention, in the step (b), a first treatment for causing the insulating paste to flow into the inner peripheral surface from the first opening side is performed zero or more times, and the insulating paste is The second treatment for flowing into the inner peripheral surface from the second opening side is performed one or more times, and the total amount of the insulating paste covering the inner peripheral surface by the second treatment is applied to the inner peripheral surface by the first treatment. You may increase more than the total amount of the insulating paste to coat | cover. As described above, when the first treatment is performed, the insulating paste tends to swell on the second region side, and when the second treatment is performed, the first region side tends to swell. Therefore, by increasing the total amount of the insulating paste that covers the inner peripheral surface in the second process as compared with the first process, the height of the raised portion of the unfired insulating layer in the first region is likely to increase. Therefore, it is possible to relatively easily form an unsintered insulating layer satisfying the distance D1 <distance D2, and to suppress partial insulation of the conductor by the insulating layer in the through hole. Note that the number of times of the first processing may be zero, but it is preferable to be one or more times. By performing the first treatment at least once, it is possible to further suppress the insulation of the second region (particularly the end portion on the second opening side) from becoming insufficient. Further, in the step (b), the total number of insulating pastes covering the inner peripheral surface in the second process is increased by increasing the number of times of performing the second process more than the number of times of performing the first process. You may increase more than the total amount of the insulating paste which coat | covers the said internal peripheral surface by 1st process. By doing this, it is not necessary to change the amount of the insulating paste used for one process between the first process and the second process, and therefore the process is easy to perform.

  In the method for manufacturing a sensor element of the present invention, in the step (a), the green structure having a chamfered portion formed on at least one of an edge of the first opening and an edge of the second opening may be prepared. Good. Since the end portion on the first opening side of the unfired insulating layer is likely to be thick because the chamfered portion is formed at the edge of the first opening, the insulating layer at the end portion on the first opening side in the through hole It can suppress that the insulation of the conductor by becomes inadequate. Similarly, with respect to the chamfered portion of the edge of the second opening, it is possible to suppress insufficient insulation of the conductor by the insulating layer at the end portion on the second opening side in the through hole.

  In the method for manufacturing a sensor element of the present invention, in the step (b), the covering may be performed so that the distance D3 (= distance D2−distance D1) ≧ 3.0 μm. In this way, by increasing the height of the raised portion of the unfired insulating layer in the first region, it is possible to prevent partial insulation of the conductor by the insulating layer in the through hole described above. The effect to do is acquired more reliably.

The sensor element of the present invention is
A laminate in which a through-hole penetrating one or more layers is formed;
A conductor filled in the through hole;
Covers the inner peripheral surface of the through hole and is disposed between the inner peripheral surface and the conductor, and in a cross-sectional view along the central axis of the through hole, a direction perpendicular to the central axis is a height direction The difference D4 between the highest point and the lowest point in the height direction is 0 μm or more and less than 5.0 μm,
It is equipped with.

  The sensor element has an insulating layer that covers the inner peripheral surface of the through hole and is disposed between the inner peripheral surface and the conductor. In this insulating layer, the difference D4 between the highest point and the lowest point in the height direction is 0 μm or more and less than 5.0 μm. That is, the boundary between the insulating layer and the conductor has a relatively flat shape. Therefore, the sensor element of the present invention can suppress the partial insulation of the conductor by the insulating layer in the through hole. Such a sensor element can be obtained, for example, by the above-described method for manufacturing a sensor element of the present invention. In this case, the sensor element of the present invention may include a fixing portion that fixes the gas sensor element, and a protective cover that covers one end of the gas sensor element in the longitudinal direction.

The gas sensor of the present invention is
The sensor element manufactured by the manufacturing method of the present invention according to any one of the aspects described above, or the sensor element of the present invention described above,
It is equipped with.

  This gas sensor includes the sensor element of the present invention according to any one of the aspects described above. Therefore, the same effect as the above-described method for producing the sensor element of the present invention or the sensor element of the present invention can be obtained. For example, the gas sensor of the present invention can suppress partial insulation of the conductor by the insulating layer in the through hole.

1 is a longitudinal sectional view of a gas sensor 100. FIG. FIG. 3 is a schematic cross-sectional view of the sensor element 101. The enlarged cross-sectional schematic diagram of the through-hole 73 periphery. Explanatory drawing of distance D4. Explanatory drawing which shows a mode that the unbaking insulating layer 96c and the unbaking conductor 97a are formed. Explanatory drawing which shows a mode that the unsintered insulating layer 96c of a modification is formed. Explanatory drawing which shows a mode that the unsintered insulating layer 96c of a modification is formed. Explanatory drawing of the green structure of the modification in which the chamfered parts 73f and 73g were formed.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a gas sensor 100 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the sensor element 101. FIG. 3 is an enlarged schematic sectional view around the through hole 73 of the sensor element 101. The sensor element 101 has a long rectangular parallelepiped shape. The longitudinal direction of the sensor element 101 (left-right direction in FIG. 2) is the front-rear direction, and the thickness direction of the sensor element 101 (up-down direction in FIG. 2) is vertical. The direction. The width direction of sensor element 101 (the direction perpendicular to the front-rear direction and the up-down direction) is the left-right direction. Moreover, the structure of the gas sensor 100 as shown in FIG. 1 is well-known, for example, it describes in Unexamined-Japanese-Patent No. 2012-210637.

The gas sensor 100 includes a sensor element 101, a protective cover 110 that covers and protects the front end side (the lower end side in FIG. 1) that is one end side in the longitudinal direction of the sensor element 101, and an element sealing body that encloses and fixes the sensor element 101 120 (corresponding to the fixing portion of the present invention) and a nut 130 attached to the element sealing body 120. This gas sensor 100 is attached to a pipe 140 such as an exhaust gas pipe of a vehicle as shown in the figure, and is used to measure the concentration of a specific gas such as NOx or O ₂ contained in the exhaust gas as the gas to be measured. . In the present embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration.

  The protective cover 110 includes a bottomed cylindrical inner protective cover 111 that covers one end of the sensor element 101, and a bottomed cylindrical outer protective cover 112 that covers the inner protective cover 111. The inner protective cover 111 and the outer protective cover 112 are formed with a plurality of holes for allowing the gas to be measured to flow through the protective cover 110. One end of the sensor element 101 is disposed in a space surrounded by the inner protective cover 111.

  The element sealing body 120 includes a cylindrical metal shell 122, a ceramic supporter 124 sealed in a through hole inside the metal shell 122, and a talc or the like sealed in a through hole inside the metal shell 122. And a green compact 126 formed of ceramic powder. The sensor element 101 is located on the central axis of the element sealing body 120 and penetrates the element sealing body 120 in the front-rear direction. The green compact 126 is compressed between the metal shell 122 and the sensor element 101. Thereby, the green compact 126 seals the through hole in the metal shell 122 and fixes the sensor element 101.

  The nut 130 is fixed coaxially with the metal shell 122, and has an external thread portion on the outer peripheral surface. The male screw portion of the nut 130 is inserted into a mounting member 141 welded to the pipe 140 and provided with a female screw portion on the inner peripheral surface. As a result, the gas sensor 100 can be fixed to the pipe 140 in a state where one end of the sensor element 101 and the portion of the protective cover 1100 protrude into the pipe 140.

As shown in FIG. 2, the sensor element 101 includes a first substrate layer 1, a second substrate layer 2, and a third substrate layer 3 each made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). The first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 are elements having a structure in which the layers are laminated in this order from the bottom in the drawing. The solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured, for example, by performing predetermined processing and circuit pattern printing on a ceramic green sheet corresponding to each layer, stacking them, and firing and integrating them.

  One end portion (front end portion) of the sensor element 101, and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the gas inlet 10 and the first diffusion In a mode in which the rate-limiting portion 11, the buffer space 12, the second diffusion-controlling portion 13, the first internal space 20, the third diffusion-controlling portion 30, and the second internal space 40 are communicated in this order. Adjacently formed.

  The gas introduction port 10, the buffer space 12, the first internal space 20, and the second internal space 40 are provided on the lower surface of the second solid electrolyte layer 6 with the upper portion provided in a state in which the spacer layer 5 is cut out. The space inside the sensor element 101 is defined by the lower part being the upper surface of the first solid electrolyte layer 4 and the side parts being the side surfaces of the spacer layer 5.

  Each of the first diffusion rate controlling unit 11, the second diffusion rate controlling unit 13, and the third diffusion rate controlling unit 30 is provided as two horizontally long slits (the opening has a longitudinal direction in a direction perpendicular to the drawing). . In addition, the site | part from the gas inlet 10 to the 2nd internal space 40 is also called a gas distribution part.

  Further, at a position farther from the front end side than the gas circulation part, the side part is partitioned by the side surface of the first solid electrolyte layer 4 between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5. The reference gas introduction space 43 is provided at the position. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

  The air introduction layer 48 is a layer made of porous ceramics, and a reference gas is introduced into the air introduction layer 48 through the reference gas introduction space 43. The air introduction layer 48 is formed so as to cover the reference electrode 42.

  The reference electrode 42 is an electrode formed in such a manner that it is sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, the reference electrode 42 leads to the reference gas introduction space 43. An air introduction layer 48 is provided. Further, as will be described later, it is possible to measure the oxygen concentration (oxygen partial pressure) in the first internal space 20 and the second internal space 40 using the reference electrode 42.

  In the gas circulation part, the gas inlet 10 is a part opened to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion control unit 11 is a part that provides a predetermined diffusion resistance to the gas to be measured taken from the gas inlet 10. The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate controlling unit 11 to the second diffusion rate controlling unit 13. The second diffusion rate limiting unit 13 is a part that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20. When the gas to be measured is introduced from the outside of the sensor element 101 to the inside of the first internal space 20, the pressure fluctuation of the gas to be measured in the external space (exhaust pressure pulsation if the gas to be measured is an automobile exhaust gas) ), The gas to be measured that is suddenly taken into the sensor element 101 from the gas inlet 10 is not directly introduced into the first internal space 20, but the first diffusion control unit 11, the buffer space 12, the second After the concentration variation of the gas to be measured is canceled through the diffusion control unit 13, the gas is introduced into the first internal space 20. As a result, the concentration fluctuation of the gas to be measured introduced into the first internal space 20 becomes almost negligible. The first internal space 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate limiting unit 13. The oxygen partial pressure is adjusted by the operation of the main pump cell 21.

  The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode portion 22a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal space 20, and an upper surface of the second solid electrolyte layer 6. An electrochemical pump cell comprising an outer pump electrode 23 provided in a manner exposed to the external space in a region corresponding to the ceiling electrode portion 22a, and a second solid electrolyte layer 6 sandwiched between these electrodes. is there.

  The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that define the first inner space 20, and the spacer layer 5 that provides side walls. Yes. Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal space 20, and a bottom portion is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. Spacer layers in which the electrode portions 22b are formed and the side electrode portions (not shown) constitute both side walls of the first internal space 20 so as to connect the ceiling electrode portions 22a and the bottom electrode portions 22b. 5 is formed on the side wall surface (inner surface), and is disposed in a tunnel-shaped structure at the portion where the side electrode portion is disposed.

The inner pump electrode 22 and the outer pump electrode 23 are formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO ₂ containing 1% of Au). The inner pump electrode 22 in contact with the gas to be measured is formed using a material that has a reduced reduction ability for the NOx component in the gas to be measured.

  In the main pump cell 21, a desired pump voltage Vp 0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and the pump current is positive or negative between the inner pump electrode 22 and the outer pump electrode 23. By flowing Ip0, oxygen in the first internal space 20 can be pumped into the external space, or oxygen in the external space can be pumped into the first internal space 20.

  Further, in order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The third substrate layer 3 and the reference electrode 42 constitute an electrochemical sensor cell, that is, a main pump control oxygen partial pressure detection sensor cell 80.

  By measuring the electromotive force V0 in the main pump control oxygen partial pressure detection sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be known. Further, the pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 of the variable power source 25 so that the electromotive force V0 is constant. Thereby, the oxygen concentration in the first internal space 20 can be kept at a predetermined constant value.

  The third diffusion control unit 30 provides a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, and the gas under measurement is supplied to the gas under measurement. This is the part that leads to the second internal space 40.

  The second internal space 40 is provided as a space for performing a process related to the measurement of the nitrogen oxide (NOx) concentration in the gas to be measured introduced through the third diffusion control unit 30. The NOx concentration is measured mainly in the second internal space 40 in which the oxygen concentration is adjusted by the auxiliary pump cell 50, and further by measuring the pump cell 41 for measurement.

  In the second internal space 40, after the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal space 20, the auxiliary pump cell 50 is further supplied to the gas to be measured introduced through the third diffusion control unit 30. The oxygen partial pressure is adjusted by the above. Thereby, since the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, the gas sensor 100 can measure the NOx concentration with high accuracy.

  The auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, and an outer pump electrode 23 (outer pump electrode 23). The auxiliary electrochemical pump cell is configured by the second solid electrolyte layer 6 and the sensor element 101 and an appropriate electrode on the outside.

  The auxiliary pump electrode 51 is disposed in the second internal space 40 in the same tunnel configuration as the inner pump electrode 22 provided in the first internal space 20. That is, the ceiling electrode portion 51 a is formed on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and the second solid electrolyte layer 4 that provides the bottom surface of the second internal space 40 is formed on the second solid electrolyte layer 6. The bottom electrode part 51b is formed, and the side electrode part (not shown) connecting the ceiling electrode part 51a and the bottom electrode part 51b is provided on the spacer layer 5 that provides the side wall of the second internal space 40. It has a tunnel-type structure formed on both wall surfaces. Note that the auxiliary pump electrode 51 is also formed using a material having a reduced reducing ability with respect to the NOx component in the gas to be measured, like the inner pump electrode 22.

  In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere in the second internal space 40 is pumped to the external space, or It is possible to pump into the second internal space 40 from the space.

  Further, in order to control the oxygen partial pressure in the atmosphere in the second internal space 40, the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte. The layer 4 and the third substrate layer 3 constitute an electrochemical sensor cell, that is, an auxiliary pump control oxygen partial pressure detection sensor cell 81.

  The auxiliary pump cell 50 performs pumping by the variable power source 52 that is voltage-controlled based on the electromotive force V1 detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. Thereby, the oxygen partial pressure in the atmosphere in the second internal space 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

  At the same time, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor cell 80, and the electromotive force V0 is controlled, so that the third diffusion rate limiting unit 30 controls the second internal space. The gradient of the oxygen partial pressure in the gas to be measured introduced into the gas 40 is controlled so as to be always constant. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

  The measurement pump cell 41 measures the NOx concentration in the gas to be measured in the second internal space 40. The measurement pump cell 41 includes a measurement electrode 44 provided on a top surface of the first solid electrolyte layer 4 facing the second internal space 40 and spaced from the third diffusion rate-determining portion 30, an outer pump electrode 23, The electrochemical pump cell is constituted by the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4.

  The measurement electrode 44 is a porous cermet electrode. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere in the second internal space 40. Further, the measurement electrode 44 is covered with a fourth diffusion rate controlling part 45.

  The 4th diffusion control part 45 is a film | membrane comprised with a ceramic porous body. The fourth diffusion control unit 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44 and also functions as a protective film for the measurement electrode 44. In the measurement pump cell 41, oxygen generated by the decomposition of nitrogen oxides in the atmosphere around the measurement electrode 44 can be pumped out, and the generated amount can be detected as the pump current Ip2.

  In order to detect the oxygen partial pressure around the measurement electrode 44, an electrochemical sensor cell, that is, a first solid electrolyte layer 4, a third substrate layer 3, a measurement electrode 44, and a reference electrode 42, that is, A measurement pump control oxygen partial pressure detection sensor cell 82 is configured. The variable power supply 46 is controlled on the basis of the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82.

The gas to be measured introduced into the second internal space 40 reaches the measurement electrode 44 through the fourth diffusion rate-determining unit 45 under the condition where the oxygen partial pressure is controlled. Nitrogen oxide in the gas to be measured around the measurement electrode 44 is reduced (2NO → N ₂ + O ₂ ) to generate oxygen. The generated oxygen is pumped by the measurement pump cell 41. At this time, the variable power source is set so that the control voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 becomes constant. 46 voltage Vp2 is controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxide in the gas to be measured, the nitrogen oxide in the gas to be measured using the pump current Ip2 in the measurement pump cell 41. The concentration will be calculated.

  In addition, if the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detecting means as an electrochemical sensor cell, The electromotive force according to the difference between the amount of oxygen generated by the reduction of the NOx component in the surrounding atmosphere and the amount of oxygen contained in the reference atmosphere can be detected, thereby the concentration of the NOx component in the gas to be measured Is also possible.

  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 constitute an electrochemical sensor cell 83. The oxygen partial pressure in the gas to be measured outside the sensor can be detected by the electromotive force Vref obtained by the sensor cell 83.

  In the gas sensor 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx). A gas to be measured is supplied to the measurement pump cell 41. Therefore, the NOx concentration in the measurement gas is determined based on the pump current Ip2 that flows when oxygen generated by the reduction of NOx is pumped out of the measurement pump cell 41 in proportion to the NOx concentration in the measurement gas. You can know.

  Furthermore, the sensor element 101 includes a heater unit 70 that plays a role of temperature adjustment for heating and maintaining the sensor element 101 in order to increase the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes a heater connector electrode 71, a heater 72, a heater lead wire 76, a through hole 73, an in-hole insulating layer 96 (corresponding to the insulating layer of the present invention), and an in-hole conductor 97 Equivalent to a conductor of the invention), a heater insulating layer 74, a lower insulating layer 69, and a pressure dissipation hole 75.

The heater 72 is an electric resistor formed in a form sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The through hole 73 is a through hole that vertically penetrates the first substrate layer 1 and the second substrate layer 2. Although not particularly limited thereto, the inner diameter of the through hole 73 is, for example, 0.3 mm to 0.8 mm. The in-hole conductor 97 is a conductor filled in the through hole 73. The heater connector electrode 71 is an electrode disposed on the lower surface of the lower insulating layer 69 disposed on the lower surface of the first substrate layer 1. The lower insulating layer 69 insulates the first substrate layer 1 and the heater connector electrode 71. The heater 72 is connected to the heater connector electrode 71 via the heater lead wire 76 and the in-hole conductor 97. The heater 72 generates heat when power is supplied from the outside through the heater connector electrode 71, and heats and keeps the solid electrolyte forming the sensor element 101. The in-hole conductor 97 is made of a material such as a noble metal such as platinum or a refractory metal such as tungsten or molybdenum.

  The heater 72 is embedded over the entire area from the first internal space 20 to the second internal space 40, and the entire sensor element 101 can be adjusted to a temperature at which the solid electrolyte is activated. ing.

  The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 by an insulator such as alumina. The heater insulating layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72 and electrical insulation between the third substrate layer 3 and the heater 72.

  The pressure dissipating hole 75 is a portion that is provided so as to penetrate the third substrate layer 3 and communicate with the reference gas introduction space 43, and is for the purpose of alleviating the increase in internal pressure accompanying the temperature increase in the heater insulating layer 74. Formed.

  The in-hole insulating layer 96 covers the inner peripheral surface of the through hole 73, and is disposed between the inner peripheral surface and the in-hole conductor 97. The in-hole conductor 97 is surrounded by an in-hole insulating layer 96 that covers the inner peripheral surface of the through hole 73, and the in-hole conductor 97 and the inner peripheral surface of the through hole 73 are insulated by the in-hole insulating layer 96. Has been. Similar to the heater insulating layer 74, the in-hole insulating layer 96 and the lower insulating layer 69 are formed of an insulator such as alumina. Although not particularly limited to this, the thickness of the in-hole insulating layer 96 is, for example, 10 μm to 30 μm.

  A portion of the sensor element 101 including the first substrate layer 1, the second substrate layer 2, the in-hole insulating layer 96, and the in-hole conductor 97 is referred to as a structure 105 (FIGS. 2 and 3). reference).

  Here, the shape of the boundary between the in-hole insulating layer 96 and the in-hole conductor 97 (see FIG. 3) will be described. FIG. 4 is an explanatory diagram of the distance D4. In FIG. 4, for the convenience of explanation, the undulation at the boundary between the in-hole insulating layer 96 and the in-hole conductor 97 is shown in an extreme shape. As shown in FIG. 4, when the direction perpendicular to the central axis 73 c (the left-right direction in FIG. 4) is the height direction in a cross-sectional view along the central axis 73 c of the through-hole 73, The difference between the highest point and the lowest point in the height direction is defined as a difference D4. A smaller difference D4 means that the boundary between the in-hole insulating layer 96 and the in-hole conductor 97 has a flat shape. The value of the distance D4 is preferably 0 μm or more and less than 5.0 μm, and more preferably 3.0 μm or less. The value of the distance D4 is measured using an image (SEM image) obtained by cutting the sensor element 101 along the central axis 73c and observing a cross section using a scanning electron microscope (SEM).

  Next, a method for manufacturing the gas sensor 100 will be described. First, a method for manufacturing the sensor element 101 will be described. First, six green ceramic green sheets containing an oxygen ion conductive solid electrolyte such as zirconia as a ceramic component are prepared. In this green sheet, a plurality of sheet holes and necessary through holes used for positioning during printing and lamination are formed in advance. And each corresponding to each of the 1st substrate layer 1, the 2nd substrate layer 2, the 3rd substrate layer 3, the 1st solid electrolyte layer 4, the spacer layer 5, and the 2nd solid electrolyte layer 6, Pattern printing and drying are performed to form various patterns on the ceramic green sheet. Specifically, the pattern to be formed is, for example, a pattern of each electrode, each insulating layer, or the heater unit 70 described above. Pattern printing is performed by applying a pattern forming paste prepared according to the characteristics required for each object to be formed on a green sheet using a known screen printing technique. At this time, the unfired insulating layer 96 to be the in-hole insulating layer 96 and the unfired conductor 97 to be the in-hole conductor 97 are formed, which will be described later. The drying process is also performed using a known drying means. When pattern printing / drying is completed, printing / drying processing of an adhesive paste for laminating / bonding the green sheets corresponding to each layer is performed. Then, the green sheets on which the adhesive paste is formed are stacked in a predetermined order while being positioned by the sheet holes, and are pressed by applying predetermined temperature and pressure conditions, thereby performing a pressing process to form a single laminate. The laminated body thus obtained includes a plurality of sensor elements 101. The laminated body is cut and cut into the size of the sensor element 101. Then, the cut laminate is fired at a predetermined firing temperature to obtain the sensor element 101.

  Here, in the manufacturing method of the sensor element 101 described above, steps (a) to (d) relating to the formation of the in-hole insulating layer 96 and the in-hole conductor 97 will be described in detail. FIG. 5 is an explanatory diagram showing a state in which the unsintered insulating layer 96c and the unsintered conductor 97a are formed.

  First, in the step (a), as shown in FIG. 5A, a through-hole having a plurality of green sheets 1a and 2a and having a first opening 73a and a second opening 73b opposite to the first opening 73a. A green structure 105a in which holes 73 are formed is prepared. In step (a), a green structure 105a prepared in advance may be prepared, or may be prepared by manufacturing the green structure 105a. When the green structure 105a is manufactured, first, two green sheets 1a and 2a (two of the six ceramic green sheets described above) that become the first substrate layer 1 and the second substrate layer 2 after firing are formed. ). Subsequently, through holes to be through holes 73 are formed in each of the green sheets 1a and 2a by a punching process using a punch of a press machine, for example. Next, the green sheets 1a and 2a are joined in the thickness direction via an adhesive layer. Thereby, the green structure 105a in which the through hole 73 is formed is obtained. In the present embodiment, the opening on the green sheet 1a side (lower side in FIG. 5) of the through hole 73 is the first opening 73a, and the opening on the green sheet 2a side (upper side in FIG. 5) of the through hole 73 is the second opening. Let it be the opening 73b. The through hole 73 may be formed after the green sheets 1a and 2a are joined.

  Subsequently, in the step (b), the inner peripheral surface of the through hole 73 is covered with an insulating paste to form an unfired insulating layer 96c. In the present embodiment, the unbaked insulating layer 96c is formed by performing the process of applying the insulating paste on the inner peripheral surface of the through hole 73 twice. First, as shown in FIG. 5B, a process (referred to as a first process) for causing the insulating paste 96a to flow into the inner peripheral surface of the through hole 73 from the first opening 73a side is performed. In addition, the white arrow of FIG.5 (b) has shown the inflow direction of the insulating paste 96a. In the first treatment, first, an insulating paste 96a is supplied to the vicinity of the first opening 73a on the lower surface of the green structure 105a. Subsequently, by making the space on the second opening 73b side negative, the insulating paste 96a is sucked from the first opening 73a side to the inner peripheral surface of the through hole 73 while sucking the inside of the through hole 73 from the second opening 73b side. To flow into. Thereby, the insulating paste 96 a is applied to the inner peripheral surface of the through hole 73. In the first treatment, portions other than the first opening 73a on the lower surface of the green sheet 1a may be masked so that the insulating paste 96a does not adhere to the lower surface of the green sheet 1a. In this case, the insulating paste 96a may be supplied on the mask.

  Subsequently, as shown in FIG. 5C, a process (referred to as a second process) for causing the insulating paste 96b to flow into the inner peripheral surface of the through hole 73 from the second opening 73b side is performed. In addition, the white arrow of FIG.5 (c) has shown the inflow direction of the insulating paste 96b. In the second treatment, first, an insulating paste 96b is supplied near the second opening 73b on the upper surface of the green structure 105a. Subsequently, the space on the first opening 73a side is set to a negative pressure, so that the insulating paste 96b is sucked from the second opening 73a side to the inner peripheral surface of the through hole 73 while sucking the inside of the through hole 73 from the first opening 73a side. To flow into. As a result, the insulating paste 96b is applied to the inner peripheral surface of the through hole 73 so as to overlap the insulating paste 96a, and the unfired insulating layer 96c including the insulating pastes 96a and 96b is formed. Similar to the first process, in the second process, a portion of the upper surface of the green sheet 2a other than the second opening 73b may be masked.

  In the step (b), in forming the unfired insulating layer 96c in this manner, the inner peripheral surface of the through hole 73 is covered with the insulating pastes 96a and 96b so that the distance D1 <the distance D2. Hereinafter, the distance D1 and the distance D2 will be described. As shown in FIG. 5C, in a cross-sectional view along the central axis 73c of the through hole 73, the direction perpendicular to the central axis 73c (the left-right direction in FIG. 5) is the height direction, and the axis in the through hole 73 From the center of the direction 73c, the first opening 73a side is defined as a first region 73d, and the second opening 73b side is defined as a second region 73e. The shortest distance in the height direction between the unsintered insulating layer 96c and the central axis 73c in the first region 73d is defined as a distance D1. The shortest distance in the height direction between the unfired insulating layer 96c and the central axis 73c in the second region 73e is a distance D2. As can be seen from FIG. 5C, the distance D1 becomes smaller as the height of the most raised portion of the unfired insulating layer 96c in the first region 73d is higher (closer to the central axis 73c). . Similarly, the distance D2 becomes smaller as the height of the most raised portion of the unfired insulating layer 96c in the second region 73e is higher (closer to the central axis 73c). In FIG. 5C, the unfired insulating layer 96c in the first region 73d has a raised portion that bulges inward in the radial direction of the through hole 73 compared to the unfired insulating layer 96c in the second region 73e. , Distance D1 <distance D2. Note that the values of the distance D1 and the distance D2 are values obtained by cutting the green structure 105 after performing the step (b) along the central axis 73c and using the SEM image of the cross section similarly to the distance D4. To do.

  In addition, as a method of forming the unbaked insulating layer 96c so that the distance D1 <the distance D2 in the step (b), for example, an insulating paste having a higher viscosity than that of the first process is used in the second process. It is done. Here, when the first treatment is performed, the insulating paste 96a tends to rise on the second region 73e side (see FIG. 5B), and when the second treatment is performed, the insulating paste 96b tends to rise on the first region 73d side. (See FIG. 5 (c)). Then, by using an insulating paste having a higher viscosity in the second process than in the first process, the height of the raised portion of the unbaked insulating layer 96c in the first region 73d is likely to increase. The insulating paste may be adjusted, for example, to a viscosity at room temperature within a range of 10 [Pa · s] to 70 [Pa · s]. In addition, when performing the first treatment and the second treatment, if the suction force is too strong, the amount of the insulating paste that passes through the through hole increases, and the height of the raised portion may be lowered. is there. Therefore, in the second process, the suction force may be weaker than that in the first process. For example, the suction force may be adjusted by adjusting the air pressure in the space on the suction side within a range of 0.2 MPa to 0.8 MPa. Further, when the first process and the second process are performed, the height of the raised portion tends to increase as the amount of the insulating paste that flows into the through hole 73 and covers the inner peripheral surface increases. Therefore, even if the amount of the insulating paste 96b that covers the inner peripheral surface of the through hole 73 in the second process is larger than the amount of the insulating paste 96a that covers the inner peripheral surface of the through hole 73 in the first process. Good. In this way, the unsintered insulating layer 96c satisfying the distance D1 <distance D2 is obtained by making at least one of the viscosity, the suction force, and the amount of the insulating paste different between the first process and the second process. Can be formed relatively easily.

  In the step (b), the unfired insulating layer 96c may be formed so that the distance D1 <distance D2, that is, the distance D3 (= distance D2-distance D1)> 0, but the distance D3 ≧ 3.0 μm. Thus, it is more preferable to form the unsintered insulating layer 96c. It should be noted that the upper limit of the distance D3 is such that the insulation performance of the in-hole insulating layer 96 and the conduction by the in-hole conductor 97 are sufficient, and the diameter of the through-hole 73 and the diameter of the in-hole conductor 97 to be formed (thick). And the thickness of the in-hole insulating layer 96 to be formed. The distance D3 may be 5.0 μm or less. Further, the closest portion 96d that is the portion closest to the central axis 73c in the unfired insulating layer 96c in the first region 73d (in FIG. 5C, the raised portion of the unfired insulating layer 96c in the first region 73d). The apex) is preferably located in a region from the center in the axial direction of the first region 73d to the first opening 73a (a quarter region close to the first opening 73a in the axial direction in the through hole 73).

  In the step (c), after the step (b), a conductive paste is filled into the through hole 73 from the first opening 73a side to form an unfired conductor 97a (FIG. 5D). In addition, the white arrow of FIG.5 (d) has shown the filling direction of the electrically conductive paste. For example, the conductive paste may be adjusted so that the viscosity at room temperature is in the range of 4000 [Pa · s] to 8000 [Pa · s]. This step (c) is performed as follows, for example. First, a metal mask (not shown) having a through hole is prepared. Subsequently, the through hole of the metal mask and the first opening 73a of the through hole 73 are aligned and fixed together. Next, the conductive paste is supplied to the vicinity of the through hole on the metal mask, and the squeegee is moved in the front-rear direction, for example, so that the conductive paste supplied on the metal mask flows into the through hole 73 and is filled. The unsintered conductor 97a. In addition, after that, the green structure 105a may be evenly pressed from above and below by a laminating press to make sure that the conductive paste (unfired conductor 97a) in the through hole 73 is filled.

  Here, when the conductive paste is filled from the first opening 73a side in the step (c), the unsintered insulating layer 96c in the first region 73d is moved with the movement of the conductive paste as compared with the second region 73e. It tends to flow toward the second opening 73b. However, in the present embodiment, the unsintered insulating layer 96c is intentionally set to satisfy the distance D1 <distance D2 in consideration of the amount that flows toward the second opening 73b. That is, the unsintered insulating layer 96c is formed with a raised portion that bulges inward in the radial direction of the through hole 73 from the second region 73e in the first region 73d. As a result, compared with the case where such a bulging portion has not been formed in advance (distance D1 ≧ distance D2), the unfired insulating layer 96c and the unfired conductor 97a after the step (c) The boundary of is a relatively flat shape as shown in FIG.

  After the steps (b) and (c) are performed to form the unfired insulating layer 96c and the unfired conductor 97a in the through hole 73, in the step (d), the green structure 105a is fired to form the unfired insulating layer. A sensor element 101 having a structure 105 in which 96c is an in-hole insulating layer 96 (corresponding to the insulating layer of the present invention) and the unfired conductor 97a is an in-hole conductor 96 (corresponding to the conductor of the present invention) is obtained. . In addition, before performing a process (d), the pattern printing and drying process mentioned above is suitably performed to the green sheet | seat corresponding to each of the green structure 105a and each layer 3-6. Then, these are pressure-bonded to form one stacked body including the green structure 105 a and cut into a plurality of sensor elements 101. Thereafter, firing in the step (d) is performed to obtain the sensor element 101.

  In the sensor element 101 manufactured in this way, the boundary between the in-hole insulating layer 96 and the in-hole conductor 97 has a relatively flat shape, similar to the above-described boundary between the unfired insulating layer 96c and the unfired conductor 97a. It has become. Further, in such a manufacturing method, the value of the distance D4 described in FIG. 4 is easily set to 0 μm or more and less than 5.0 μm.

  When the sensor element 101 is obtained, the sensor element 101 is passed through the prepared supporter 124 and the thick powder 126 and inserted into the through hole inside the metal shell 122 from the upper side in FIG. Is fixed by the element sealing body 120. And the gas sensor 100 is obtained by attaching the nut 130, the protective cover 110, etc. In addition, the manufacturing method of such a gas sensor is well-known, for example, it describes in the international publication 2013/005491.

  In the manufacturing method of the sensor element 101 of the present embodiment described above, the distance D1 <the distance D2 is satisfied when the inner peripheral surface of the through hole 73 is covered with the insulating pastes 96a and 96b to form the unfired insulating layer 96c. Like that. Thereafter, a conductive paste is filled into the through hole 73 from the first opening 73a side to form an unfired conductor 97a. By doing so, the boundary between the in-hole insulating layer 96 and the in-hole conductor 97 after filling and baking of the conductive paste becomes a relatively flat shape. Therefore, it is difficult to generate a portion where the thickness of the in-hole insulating layer 96 in the through hole 73 is insufficient. Therefore, partial insulation of the in-hole conductor 97 by the in-hole insulating layer 96 in the through hole 73 can be suppressed.

  In addition, the non-fired insulating layer 96c satisfying the distance D1 <distance D2 can be formed relatively easily by using the insulating paste 96b having a higher viscosity in the second process than in the first process. By reducing the suction force in the second process as compared with the first process, the unsintered insulating layer 96c satisfying the distance D1 <distance D2 can be formed relatively easily. By increasing the total amount of the insulating paste 96b that flows into the inner peripheral surface of the through hole 73 in the second process as compared with the first process, the unfired insulating layer 96c that satisfies the distance D1 <distance D2 can be formed relatively easily. it can.

  Furthermore, by performing the coating in the step (b) so that the distance D3 (= distance D2−distance D1) ≧ 3.0 μm, the height of the raised portion of the unfired insulating layer 96c in the first region 73d is further increased. As a result, the effect of suppressing the partial insulation of the in-hole conductor 97 by the in-hole insulating layer 96 in the through hole 73 is obtained more reliably.

  Furthermore, in the sensor element 101 of the present embodiment, since the difference D4 is not less than 0 μm and less than 5.0 μm, the in-hole conductor 97 is partially insulated by the in-hole insulating layer 96 in the through hole 73. It can be suppressed from becoming insufficient.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the second process is performed after the first process is performed in the step (b), but the second process may be performed first. FIG. 6 is an explanatory view showing a state in which the unsintered insulating layer 96c of the modified example in this case is formed. As shown in the drawing, in the step (b), the second treatment is first performed to apply the insulating paste 96b to the inner peripheral surface of the through hole 73 (FIG. 6A), and then the first treatment is performed. An unfired insulating layer 96c may be formed by applying an insulating paste 96a to the inner peripheral surface of the through hole 73 (FIG. 6B). Also in this case, if the unfired insulating layer 96c is formed so that the distance D1 <the distance D2, the same effect as the above-described embodiment can be obtained.

  In the embodiment described above, the first process and the second process are performed once in the step (b). However, the present invention is not limited to this, and the first process may be performed once or more and the second process may be performed one or more times. . Also in this case, for example, at least one or more of the viscosity of the insulating paste, the suction force, and the total amount of the insulating paste is different between the first treatment and the second treatment, so that the distance D1 <distance D2 is satisfied. The insulating layer 96c may be formed. When the total amount of the insulating paste is different between the first process and the second process, the number of times of performing the second process is made larger than the number of times of performing the first process, thereby covering the inner peripheral surface with the second process. The total amount of the insulating paste 96b may be larger than the total amount of the insulating paste 96a that covers the inner peripheral surface in the first treatment. By doing this, it is not necessary to change the amount of the insulating paste used for one process between the first process and the second process, and therefore the process is easy to perform.

  In the embodiment described above, the first process and the second process are performed once in the step (b). However, if the second process is performed one or more times in the process (b), the first process is not performed. Good. FIG. 7 is an explanatory diagram showing a state in which the unsintered insulating layer 96c of the modified example in this case is formed. As shown in the drawing, in the step (b), the second treatment is performed twice, and the insulating pastes 96b1 and 96b2 are applied in this order on the inner peripheral surface of the through hole 73 to form the insulating pastes 96b1 and 96b2. An unsintered insulating layer 96c may be formed. As described above, by omitting the first process, the total amount of the insulating paste covering the inner peripheral surface in the second process is larger than the total amount (= 0) of the insulating paste covering the inner peripheral surface in the first process. Therefore, the unfired insulating layer 96c satisfying the distance D1 <distance D2 can be formed relatively easily. However, since the insulation of the second region 73e (particularly the end portion on the second opening 73b side) can be further suppressed, the first treatment is preferably performed once or more.

  In the step (a) of the embodiment described above, a green structure 105 in which a chamfered portion is formed on at least one of the edge of the first opening 73a and the edge of the second opening 73b may be prepared. FIG. 8 is an explanatory diagram of a modified green structure 105 in which chamfered portions 73f and 73g are formed. FIG. 8 shows a state after preparing the green structure 105 of a modified example in the step (a) and performing the step (b) similar to FIG. As can be seen from a comparison between FIG. 7B and FIG. 8, the chamfered portion 73f is formed at the edge of the first opening 73a, so that the end portion of the unfired insulating layer 96c on the first opening 73a side (see FIG. 8) tends to be thicker. Therefore, it is possible to suppress insufficient insulation of the in-hole conductor 97 by the in-hole insulating layer 96 at the end of the through hole 73 on the first opening 73a side. Similarly, since the chamfered portion 73g at the edge of the second opening 73b is formed, the end portion (upper end in FIG. 8) of the unfired insulating layer 96c on the second opening 73b side is likely to be thick. Therefore, it is possible to suppress insufficient insulation of the in-hole conductor 97 by the in-hole insulating layer 96 at the end of the through hole 73 on the second opening 73b side. The chamfered portions 73f and 73g are formed by C chamfering, but may be formed by R chamfering or may be formed by other chamfering. The dimension of the chamfer may be, for example, 5 μm to 50 μm (C 5 μm to C50 μm if C chamfering). Further, the chamfered portions 73f and 73g may be formed at the same time as the through hole 73 or after the through hole 73 is formed.

  In the embodiment described above, as a method of forming the unfired insulating layer 96c satisfying the distance D1 <distance D2 in the step (b), at least one of the viscosity of the insulating paste, the suction force, and the total amount of the insulating paste is the first. Although it is exemplified that the first process is different from the second process, the present invention is not limited to this. The step (b) may be any step as long as the green insulating layer 96c can be formed so as to satisfy the distance D1 <distance D2. Further, the unfired insulating layer 96c formed in the step (b) may have any shape as long as the distance D1 <the distance D2 is satisfied. For example, as shown in FIGS. 5C and 7B, the shape of the unsintered insulating layer 96c increases in the height direction with respect to the central axis 73c as the distance from the apex of the raised portion in the first region 73d increases. It may be a shape that tends to increase the distance (a shape that has one rising peak). Alternatively, as shown in FIG. 6B, the shape of the unsintered insulating layer 96c has a shape having a plurality of rising peaks (for example, one or more in each of the first region 73d and the second region 73e). It may be a shape in which a rising peak exists. Further, the shape of the unsintered insulating layer 96c may be other shapes. For example, in FIG. 5C, FIG. 6B, FIG. 7B, and FIG. 8, the peak of the raised portion of the unfired insulating layer 96c is located in the first region 73d, and the peak is closest. Although the portion 96d is formed, the apex may be located outside the first region 73 (below the first opening 73a in the drawing). In this case, since the closest part 96d is determined based on the shape of the unsintered insulating layer 96c in the first region 73d, the apex of the rising part and the closest part 96d are determined separately.

  In the embodiment described above, the through hole 73 is a through hole that vertically penetrates the first substrate layer 1 and the second substrate layer 2, but is not limited thereto. The same effect can be obtained by applying the steps (a) to (d) of the above-described embodiment to any through hole penetrating any one or more of the layers 1 to 6.

  In the above-described embodiment, the unfired insulating layer 96c is formed in the step (b). However, unfired insulating layers that become the heater insulating layer 74 and the lower insulating layer 69 may be formed at this time. For example, when the first treatment is performed, the insulating paste 96a is supplied in the vicinity of the first opening 73a, and an unfired insulating layer that becomes the lower insulating layer 69 is formed on the lower surface of the green sheet 1a by, for example, screen printing. Good. Similarly, when performing the second treatment, an insulating paste 96b is supplied near the second opening 73b, and an unfired insulating layer to be the heater insulating layer 74 is formed on the upper surface of the green sheet 2a by, for example, screen printing. Also good. However, the present invention is not limited to this, and the unfired insulating layer that becomes the heater insulating layer 74 and the lower insulating layer 69 may be formed before and after the step (b) or after the step (c).

  In the above-described embodiment, the conductive paste is filled from the first opening 73a (the lower opening of the through hole 73) in the step (c), but the conductive paste is filled from the second opening 73b (the upper opening of the through hole 73). Good. In this case, the first opening 73a corresponds to the second opening of the present invention, the second opening 73b corresponds to the first opening of the present invention, and the step (b) is an aspect in which the upper and lower sides are reversed from the above-described embodiment. Just do it.

  Hereinafter, an example in which a sensor element is specifically manufactured will be described as an example. In addition, this invention is not limited to a following example.

[Example 1]
According to the method for manufacturing the sensor element 101 of the above-described embodiment, the sensor element 101 shown in FIGS. First, as the step (a), the green structure 105 shown in FIG. The green structure 105 had a length in the front-rear direction of 70 mm, a width in the left-right direction of 6 mm, and a thickness in the vertical direction (= the length in the axial direction of the through hole 73) of 300 μm. The inner diameter of the through hole 73 was 0.6 mm. In producing the green structure 105, the green sheets 1a and 2a were formed by mixing zirconia particles to which 4 mol% of a stabilizer yttria was added, an organic binder, and an organic solvent, and then forming a tape.

  Subsequently, as the step (b), the first treatment and the second treatment are performed once in this order as in the above-described embodiment (FIGS. 5B and 5C), and the unfired insulating layer 96c is obtained. Formed. The insulating paste 96a used in the first treatment was prepared by mixing alumina powder and a binder solution at a weight ratio of 1: 2 so that the viscosity at normal temperature was 20 [Pa · s]. The insulating paste 96b used in the second treatment is a mixture of alumina powder and binder solution at a weight ratio of 2: 3, and the viscosity at normal temperature is 40 [Pa · s], which is higher than that of the insulating paste 96a. Adjusted as follows. In the first treatment and the second treatment, the suction force is the same, and the pressure in the space on the suction side is 0.6 MPa. The amounts of the insulating pastes 96a and 96b used in the first process and the second process are the same. When the distance D3 (= distance D2−distance D1) of the green structure 105 after performing the step (b) in Example 1 was measured, it was 3.0 μm.

  Next, as a step (c), the conductive paste is filled into the through hole 73 from the first opening 73a side in the same manner as in the above-described embodiment to form an unfired conductor 97a (FIG. 5D). ). The conductive paste 97a was prepared by mixing platinum powder and a binder solution in a weight ratio of 25: 1 so that the viscosity at normal temperature was 6000 [Pa · s].

  After the step (c), pattern printing / drying processing is performed on the green sheet corresponding to each of the green structure 105a and each of the layers 3 to 6, and these are pressed to form one laminate including the green structure 105a. The plurality of sensor elements 101 were cut. Then, the baking of the process (d) was performed and the sensor element 101 of Example 1 was obtained. The distance D4 of the sensor element 101 of Example 1 was measured and found to be 3.0 μm.

  In the sensor element 101 of Example 1, a leak inspection of the heater unit 70 was performed. Specifically, the sensor element 101 was heated by energizing the heater 72 through the heater connector electrode 71 to a temperature of 800 ° C. After heating, a voltage of 20 V is applied between the heater 72 and the outer pump electrode 23, and then the periphery of the through hole 73 is observed, and a blackened portion is observed in both the first substrate layer 1 and the second substrate layer 2. When it was not, it was determined to be good, and when any part was blackened, it was determined to be bad. If there is a portion where the in-hole conductor 97 is not sufficiently insulated by the in-hole insulating layer 96 in the through hole 73, a voltage is applied to the first substrate layer 1 and the second substrate layer 2 to blacken them. To do. The leak test result of Example 1 was good.

[Comparative Example 1]
A sensor element 101 was manufactured in the same manner as in Example 1 except that the conductive paste was filled into the through hole 73 from the second opening 73b side in the step (c), and Comparative Example 1 was obtained. It was 5.0 micrometers when the distance D4 of the sensor element 101 of the comparative example 1 was measured. The result of the leak test of Comparative Example 1 was poor.

[Example 2]
In the step (b), the viscosity at room temperature of the insulating pastes 96a and 96b is the same (30 [Pa · s]) in the first treatment and the second treatment, and the suction in the second treatment is higher than that in the first treatment. A sensor element 101 was manufactured in the same manner as in Example 1 except that the force was weakened, and Example 2 was obtained. In the first process, the pressure in the space on the suction side was set to 0.8 MPa, and in the second process, the pressure in the space on the suction side was set to 0.2 MPa. The distance D3 in Example 2 was 3.0 μm, and the distance D4 was 3.0 μm. The leak test result of Example 2 was good.

[Comparative Example 2]
The sensor element 101 was manufactured in the same manner as in Example 2 except that the conductive paste was filled into the through hole 73 from the second opening 73b side in Step (c), and Comparative Example 2 was obtained. When the distance D4 of the sensor element 101 of Comparative Example 2 was measured, it was 10.0 μm. The result of the leak test of Comparative Example 2 was poor.

[Example 3]
A sensor element 101 is manufactured in the same manner as in Example 1 except that the order of the first process and the second process is reversed in the step (b) (second process → first process). did. The distance D3 in Example 3 was 1.0 μm, and the distance D4 was 2.0 μm. The result of the leak test of Example 3 was good.

[Comparative Example 3]
A sensor element 101 was manufactured in the same manner as in Example 3 except that the conductive paste was filled into the through hole 73 from the second opening 73b side in Step (c), and Comparative Example 3 was obtained. It was 11.0 micrometers when the distance D4 of the sensor element 101 of the comparative example 3 was measured. The result of the leak test of Comparative Example 3 was poor.

[Example 4]
A sensor element 101 is manufactured in the same manner as in Example 2 except that the order of the first process and the second process is reversed in the step (b) (second process → first process). did. The distance D3 in Example 4 was 1.0 μm, and the distance D4 was 2.0 μm. The result of the leak test of Example 4 was good.

[Comparative Example 4]
The sensor element 101 was manufactured in the same manner as in Example 4 except that the conductive paste was filled into the through hole 73 from the second opening 73b side in Step (c), and Comparative Example 4 was obtained. The distance D4 of the sensor element 101 of Comparative Example 4 was measured and found to be 11.0 μm. The leak test result of Comparative Example 4 was poor.

[Example 5]
In step (b), the sensor element 101 was manufactured in the same manner as in Example 2 except that the first process was not performed and the second process was performed twice as in FIG. In Example 5, the distance D3 was 4.0 μm, and the distance D4 was 2.5 μm. The result of the leak test of Example 5 was good.

[Comparative Example 5]
A sensor element 101 was manufactured in the same manner as in Example 5 except that the conductive paste was filled into the through hole 73 from the second opening 73b side in the step (c), and Comparative Example 5 was obtained. The distance D4 of the sensor element 101 of Comparative Example 5 was measured and found to be 10.5 μm. The result of the leak test of Comparative Example 5 was poor.

[Example 6]
In the step (a), the sensor element 101 is manufactured and implemented in the same manner as in Example 5 except that the green structure 105a in which the chamfered portions 73f and 73g are formed in the through hole 73 is prepared in the same manner as in FIG. Example 6 was adopted. The dimensions of the chamfered portions 73f and 73g were C5.0 μm. The distance D3 in Example 6 was 4.0 μm, and the distance D4 was 2.5 μm. The result of the leak test of Example 6 was good. Of the in-hole insulating layer 96, the average film thickness of the portion formed on the inner peripheral surface of the through hole 73 other than the chamfered portions 73f and 73g was 20 μm. Of the in-hole insulating layer 96, the film thickness at the end on the first opening 73a side was 25 μm, which was thicker than this average film thickness. Of the in-hole insulating layer 96, the thickness of the end portion on the second opening 73b side was 23 μm, which was thicker than this average thickness.

[Comparative Example 6]
A sensor element 101 was manufactured in the same manner as in Example 6 except that the conductive paste was filled into the through hole 73 from the second opening 73b side in Step (c), and Comparative Example 6 was obtained. When the distance D4 of the sensor element 101 of Comparative Example 5 was measured, it was 10.8 μm. The result of the leak test of Comparative Example 6 was poor.

[Measurement of defective rate]
About Examples 1-6 and Comparative Examples 1-6, 50 sensor elements were produced, respectively, and the defect rate of the leak test was measured. Table 1 shows the distances D3 and D4 and the leak inspection defect rates of Examples 1 to 6 and Comparative Examples 1 to 6. As shown in Table 1, all of Examples 1 to 6 had a defect rate of 0%. Further, in Comparative Examples 1 to 6 in which the distance D4 is 5 μm or more, defects occurred in at least some of the plurality, and the comparative examples with larger distances D3 and D4 tended to have a higher defect rate.

[Examples 7 to 10]
A sensor element 101 was produced in the same manner as in Example 1 except that the viscosity at normal temperature of the conductive paste was variously changed from 6000 [Pa · s], and Examples 7 to 10 were obtained. Specifically, the viscosity at normal temperature of the conductive paste is 4000 [Pa · s] in Example 7, 8000 [Pa · s] in Example 8, 2000 [Pa · s] in Example 9, In Example 10, it was set to 10,000 [Pa · s]. Fifty sensor elements of Examples 7 to 10 were produced, respectively, and the defect rate of leak inspection was measured. Table 2 shows the viscosity of conductive paste, distances D3 and D4, and the defect rate of leak inspection in Examples 7 to 10. Table 2 also shows the results of Example 1. In Example 9 in which the viscosity of the conductive paste was 2000 [Pa · s], the shrinkage (dent) occurred due to the large shrinkage amount of the conductive paste after drying, and the hole after firing in the through hole 73. There was a tendency that the amount of the inner conductor 96 was insufficient. Therefore, 16% of the manufactured sensor elements 101 were defective in manufacturing. For the remaining 84%, although the shrinkage occurred, the leak inspection result was good (the defect rate was 0%). In Example 10 in which the viscosity of the conductive paste was 10,000 [Pa · s], about 20% of the sensor elements 101 that were manufactured, the conductive paste could be filled into the through holes 73 in the first place. There wasn't. For the remaining 80%, the conductive paste was appropriately filled in the through hole 73, and in all cases, the result of the leak inspection was good (the defect rate was 0%). From the above results and Table 2, all of Examples 7 to 10 have good leak test results, but the viscosity at normal temperature of the conductive paste is preferably more than 2000 [Pa · s] from the viewpoint of manufacturing. It is considered that 4000 [Pa · s] or more is more preferable. Further, the viscosity of the conductive paste at normal temperature is preferably less than 10,000 [Pa · s], and more preferably 8000 [Pa · s] or less.

[Example 11, Comparative Example 7]
Except that the inner diameter of the through hole 73 was variously changed from 0.6 mm, the sensor element 101 was manufactured in the same manner as in Example 1 to obtain Example 11 and Comparative Example 7. Specifically, the inner diameter of the through hole 73 was 0.5 mm in Example 11 and 0.4 mm in Comparative Example 7. When 50 sensor elements of Example 11 were manufactured and the defect rate of the leak test was measured, the defect rate was 0%. Further, in Comparative Example 7, since the diameter of the through hole 73 was small, the conductive paste could not be filled and the sensor element could not be manufactured. Table 3 shows the viscosity of the conductive paste, the inner diameter of the through hole, the distances D3 and D4, and the defect rate of the leak test in Example 11 and Comparative Example 7. Table 3 also shows the results of Example 1. From the above results and Table 3, it is considered that the inner diameter of the through hole 73 is preferably more than 0.4 mm, and more preferably 0.5 mm or more because the conductive paste is easily filled. For example, by adjusting the filling conditions such as adjusting the viscosity of the conductive paste to a value smaller than 6000 [Pa · s], the conductive paste is conductive even if the inner diameter of the through hole 73 is 0.4 mm or less. In some cases, an adhesive paste can be filled.

[Measurement method of viscosity]
In the examples and comparative examples described above, the viscosities of the insulating paste and the conductive paste were measured using an E-type viscometer (MCR-102 manufactured by Anton Paar). More specifically, the viscosity of the insulating paste is treated for 30 seconds with a cone rotation speed of 30 [1 / second], then treated for 60 seconds with a cone rotation speed of 10 [1 / second], Then, a measurement sequence was performed in which the cone rotation speed was 1 [1 / second] for 90 seconds, and the average value was measured for the last 5 seconds. The viscosity of the conductive paste was measured by performing a measurement sequence of 180 seconds with a cone rotation speed of 10 [1 / second] and then 240 seconds with a cone rotation speed of 1 [1 / second]. Measured as an average value over 5 seconds.

  DESCRIPTION OF SYMBOLS 1 1st board | substrate layer, 1a green sheet, 2nd board | substrate layer, 2a green sheet, 3rd board | substrate layer, 4th 1st solid electrolyte layer, 5 spacer layer, 6 2nd solid electrolyte layer, 7a-7e adhesive layer, 8 Green Structure, 10 Gas Inlet, 11 First Diffusion Controlling Part, 12 Buffer Space, 13 Second Diffusion Controlling Part, 20 First Internal Space, 21 Main Pump Cell, 22 Inner Pump Electrode, 22a Ceiling Electrode Part, 22b Bottom electrode portion, 23 Outer pump electrode, 25 Variable power source, 30 Third diffusion rate limiting portion, 40 Second internal space, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 45 Fourth diffusion Control part, 46 Variable power supply, 48 Air introduction layer, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 51a Ceiling electrode part, 51b Bottom electrode part, 52 Variable power supply, 6 9 Lower insulating layer, 69a Unsintered insulating layer, 70 Heater part, 71 Heater connector electrode, 72 Heater, 73 Through hole, 73a 1st opening, 73b 2nd opening, 73c Center axis, 73d 1st area | region, 73e 2nd area | region 73f, 73g chamfered portion, 74 heater insulating layer, 74a unfired insulating layer, 75 pressure dissipation hole, 76 heater lead wire, 80 oxygen partial pressure detection sensor cell for main pump control, 81 oxygen partial pressure detection sensor cell for auxiliary pump control 82, oxygen sensor for detecting pump partial pressure for measuring pump, 83 sensor cell, 96 in-hole insulating layer, 96a, 96b, 96b1, 96b2 insulating paste, 96c unsintered insulating layer, 96d closest part, 97 in-hole conductor, 97a Unsintered conductor, 100 gas sensor, 101 sensor element, 105 structure, 10 5a Green structure, 110 protective cover, 111 inner protective cover, 112 outer protective cover, 120 element sealing body, 122 metal shell, 124 supporter, 126 green compact, 130 nut, 140 pipe, 141 mounting member.

Claims (8)

(A) A green structure having a single green sheet or a plurality of stacked green sheets and having a first opening and a through hole having a second opening opposite to the first opening is prepared. Process,
(B) A step of forming an unsintered insulating layer by coating the inner peripheral surface of the through hole with an insulating paste, in a direction perpendicular to the central axis in a sectional view along the central axis of the through hole The first opening side from the center of the axial direction in the through hole as a first region, the second opening side as a second region, and the unsintered insulating layer in the first region When the shortest distance in the height direction from the central axis is a distance D1, and the shortest distance in the height direction between the green insulating layer in the second region and the central axis is a distance D2, the distance Performing the coating so that D1 <distance D2.
(C) after the step (b), filling the through hole with a conductive paste from the first opening side to form an unfired conductor;
(D) after the step (c), firing the green structure to obtain a sensor element having a structure in which the unsintered insulating layer becomes an insulating layer and the unsintered conductor becomes a conductor; ,
A method for manufacturing a sensor element including: In the step (b), a first treatment for causing the insulating paste to flow into the inner peripheral surface from the first opening side, and a second process for causing the insulating paste to flow into the inner peripheral surface from the second opening side. And the treatment is performed at least once, and the second treatment uses the insulating paste having a higher viscosity than the first treatment.
A method for manufacturing the sensor element according to claim 1. In the step (b), a first process for allowing the insulating paste to flow into the inner peripheral surface from the first opening side while sucking the inside of the through hole from the second opening side; The second process of allowing the insulating paste to flow into the inner peripheral surface from the second opening side while sucking from the first opening side is performed at least once, and the second process is compared with the first process. To weaken the suction force,
The manufacturing method of the sensor element of Claim 1 or 2. In the step (b), the first treatment for causing the insulating paste to flow into the inner peripheral surface from the first opening side is performed zero or more times, and the insulating paste is applied from the second opening side to the inner peripheral surface. The second treatment to be introduced is performed at least once, and the total amount of the insulating paste covering the inner peripheral surface in the second treatment is larger than the total amount of the insulating paste covering the inner peripheral surface in the first treatment. To
The manufacturing method of the sensor element of any one of Claims 1-3. In the step (a), the green structure having a chamfered portion formed on at least one of an edge of the first opening and an edge of the second opening is prepared.
The manufacturing method of the sensor element of any one of Claims 1-4. In the step (b), the coating is performed so that the distance D3 (= distance D2−distance D1) ≧ 3.0 μm.
The manufacturing method of the sensor element of any one of Claims 1-5. A laminate in which a through-hole penetrating one or more layers is formed;
A conductor filled in the through hole;
Covers the inner peripheral surface of the through hole and is disposed between the inner peripheral surface and the conductor, and in a cross-sectional view along the central axis of the through hole, a direction perpendicular to the central axis is a height direction The difference D4 between the highest point and the lowest point in the height direction is 0 μm or more and less than 5.0 μm,
A sensor element comprising:   A gas sensor comprising the sensor element according to claim 7.

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