JP5166474B2 - Method for manufacturing ceramic device and ceramic device - Google Patents

Description

  The present invention relates to a method for manufacturing a ceramic device such as a sensor element of a gas sensor.

Conventionally, various measuring devices have been used to know the concentration of a desired gas component in a gas to be measured. For example, a gas sensor having a sensor element in which a plurality of solid electrolyte layers having oxygen ion conductivity such as zirconia (ZrO ₂ ) are stacked is known as an apparatus for measuring NOx concentration in a measurement gas such as combustion gas. is there.

  Such a sensor element is manufactured by, for example, laminating them after performing predetermined processing and circuit pattern printing on the ceramic green sheets corresponding to the respective layers, and further firing and integrating them.

  In general, multilayer ceramic devices produced by the same process as described above, including sensor elements, have a common problem that warpage may occur during firing. In order to suppress warpage during firing, generally, a plurality of ceramic green sheets used for stacking have substantially the same firing shrinkage rate. However, it is difficult to completely match the firing shrinkage rates of the ceramic green sheets, and some manufacturing variations may occur. In addition, a device obtained by firing when the laminate includes a layer made of a different material that has a different firing shrinkage rate than the ceramic green sheet, such as by applying a conductive paste to form a circuit pattern. Warp tends to occur.

  In order to suppress the occurrence of such warpage in the multilayer ceramic device, various manufacturing methods have been disclosed. For example, by sandwiching and firing the laminate with insulating ceramics having a smaller firing shrinkage rate than each ceramic green sheet, the firing shrinkage rate of each ceramic green sheet is made equal to the shrinkage rate of the insulator ceramic, and after firing A method for suppressing warpage occurring in the device is known (Patent Document 1). Also, a method of suppressing warpage that occurs during firing of the laminate by performing pressure treatment so that the outer peripheral portion of the laminate is thinner than the inside, and making the firing shrinkage rate of the periphery smaller than the inside. Is known (Patent Document 2). In addition, a method is known in which the warp once generated is eliminated by inverting the fired body obtained by the first firing and performing the second firing.

JP-A-11-55058 JP 2002-198648 A

  However, the technique disclosed in Patent Document 1 greatly shrinks the device in the direction perpendicular to the surface direction instead of suppressing the shrinkage in the surface direction of the multilayer ceramic device (the in-plane direction of the ceramic sheet). Therefore, it is impossible to use the device when it is necessary to shrink the device isotropically. In addition, since it is necessary to separately create another type of shrinkage control green sheet such as an insulating ceramic sheet, the cost increases by the amount of the shrinkage control green sheet, and a green sheet that is not necessary for the actual functioning is added. In addition, since a laminated body is formed, there is a problem that the thickness as a whole increases and it is difficult to reduce the size of the design.

Moreover, in the method of performing a pressure treatment so that the outer peripheral portion of the laminated body is made thinner than the inside disclosed in Patent Document 2, it is necessary to perform a cutting process after firing. When this method is applied to the production of a device having a strong ceramic material such as ZrO ₂ , it is necessary to deal with burrs and burrs during cutting and wear of the cutting blade, which is difficult in practice. In addition, when the device shape is reduced, the method cannot be applied to a case where a plurality of devices are taken out by a single laminate, such as dividing the green sheet laminate into individual pieces and then firing them.

  Further, the method of firing twice by turning upside down has problems that the amount of energy used and the firing time increase, thereby increasing the cost and causing firing damage to the electrode / sensor element.

  This invention is made | formed in view of the said subject, and it aims at providing the manufacturing method by which the curvature of a ceramic device is suppressed.

In order to solve the above-mentioned problems, the invention of claim 1 is a method of manufacturing a ceramic device by firing a laminate of a plurality of ceramic green sheets, and a) a ceramic green serving as a front surface and a back surface of the laminate. Only the sheet is mainly composed of alumina, and a step of applying a paste having a binding ability to the firing shrinkage behavior of the laminate during firing, and b) firing the laminate to which the paste is applied, e Bei obtaining a ceramic device by firing shrinkage in a predetermined shrinkage of the laminate restraint of a firing shrinkage behavior of the paste, and, in the step b), said step a) the paste in the The applied ceramic green sheet and another ceramic green sheet are bonded together with an adhesive paste. Upon obtaining the laminate by firing the laminate, characterized in that.

Invention of Claim 2 is a manufacturing method of the ceramic device of Claim 1, Comprising: The application area ratio of the said paste in the ceramic green sheet used as the surface and the back surface of the said laminated body in the said process a) is 68%. It is the above.

Invention of Claim 3 is a manufacturing method of the ceramic device of Claim 1 or Claim 2 , Comprising: Application | coating thickness of the said paste to the ceramic green sheet used as the surface and the back surface of the said laminated body in the said process a) Is 5 μm or more and 20 μm or less.

Invention of Claim 4 is a manufacturing method of the ceramic device in any one of Claim 1 thru | or 3 , Comprising: The ratio of the additive in the said paste in the said process a) is 3 to 20 weight% It is characterized by the following.

The invention of claim 5 is the method for manufacturing a ceramic device according to any one of claims 1 to 4 , wherein the ceramic device obtained in the step b) has a porosity of 5% on the front surface and the back surface. It is characterized by comprising a porous layer of 25% or less.

Invention of Claim 6 is a manufacturing method of the ceramic device in any one of Claims 1-5 , Comprising: The said ceramic device is a sensor element which consists of oxygen ion conductive solid electrolyte ceramics, It is characterized by the above-mentioned. To do.

According to a seventh aspect of the invention, a ceramic device is manufactured by the manufacturing method according to any one of the first to sixth aspects.

According to the first to seventh aspects of the invention, by adding a simple and low-cost process of applying a paste to a conventional ceramic device manufacturing process, a good ceramic device in which warpage is suppressed is obtained. be able to.

In particular, according to the invention of claim 5 , since the porous layer absorbs internal stress in the ceramic device, generation of cracks due to the presence of internal stress is suppressed.

2 is a schematic cross-sectional view schematically showing an example of the configuration of the sensor element 101. FIG. It is a figure which shows the flow of a process at the time of creating the sensor element. FIG. 5 is a diagram illustrating a method for measuring a warpage amount of a sensor element 101. It is a figure which lists the conditions of the sensor element which concerns on an Example, and the result of a curvature test in a list.

<Schematic configuration of sensor element>
First, a schematic configuration of the gas sensor 100 including the sensor element 101 which is an example of a ceramic device manufactured by the manufacturing method of the present invention will be described.

FIG. 1 is a schematic cross-sectional view schematically showing an example of the configuration of the sensor element 101. The sensor element 101 includes a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, and a first solid electrolyte layer 4 each made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). The spacer layer 5 and the second solid electrolyte layer 6 are elongated and long plate-like elements having a structure in which they 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 laminated on a ceramic green sheet corresponding to each layer after performing predetermined processing and printing of a circuit pattern, etc., and the resultant laminate is cut into a predetermined size and fired. And integrated.

  Furthermore, the upper and lower surfaces of the sensor element 101 (that is, the upper surface of the second solid electrolyte layer 6 and the lower surface of the first substrate layer 1) are porous materials mainly composed of alumina and having a porosity of 5% or more and 25% or less. A layer 90 is provided. More preferably, the porosity of the porous layer 90 is 10% or more and 20% or less. In the present embodiment, the porosity represents the volume fraction (volume%) of the region occupied by the pores in the porous layer 90. The porous layer 90 is a layer obtained by sintering and solidifying a warp suppressing paste applied to suppress warping during firing of the sensor element 101. Details of the suppression of the warp of the sensor element 101 by the warp suppression paste will be described later. The porous layer 90 has a function of absorbing internal stress remaining in the sensor element 101. As the porous layer 90 absorbs internal stress, in the sensor element 101, the occurrence of cracks due to the presence of internal stress is suppressed. In addition, when the porosity of the porous layer 90 is smaller than 5% or larger than 25%, the porous layer 90 may be peeled off, which is not preferable.

  One end 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, is a gas inlet 10, a first diffusion rate limiting unit 11, and a buffer space. 12, the second diffusion rate limiting part 13, the first internal space 20, the third diffusion rate limiting part 30, and the second internal space 40 are adjacently formed in such a manner that they communicate in this order.

  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 atmosphere introduction layer 48 is a layer made of porous alumina, and the reference gas is introduced into the atmosphere 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 is 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.

  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 6, the spacer layer 5, the first solid electrolyte 4, The third substrate layer 3 and the reference electrode 42 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 80 for main pump control.

  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 control of Vp0 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 the first internal space 20 in advance, the auxiliary pump cell 50 further supplies the gas to be measured introduced through the third diffusion control unit. The oxygen partial pressure is adjusted. Thereby, since the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, the gas sensor including the sensor element 101 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 first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40 is formed on the first solid electrolyte layer 4. 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 fourth diffusion rate-determining part 45 is a film composed of a porous body mainly composed of alumina (Al ₂ O ₃ ). 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 partial pressure of oxygen around the measurement electrode 44, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, The reference electrode 42 constitutes an electrochemical sensor cell, that is, a measurement pump control oxygen partial pressure detection sensor cell 82. 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. The 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.

  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 measurement electrode The electromotive force according to the difference between the amount of oxygen generated by the reduction of the NOx component in the atmosphere around 44 and the amount of oxygen contained in the reference atmosphere can be detected, whereby the NOx component in the gas to be measured It is also possible to determine the concentration of.

  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 sensor element 101 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). The measured gas 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 unit 70 includes a heater electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure dissipation hole 75.

  The heater electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1. By connecting the heater electrode 71 to an external power source, power can be supplied to the heater unit 70 from the outside.

  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 heater 72 is connected to the heater electrode 71 through the through-hole 73, generates heat when power is supplied from outside through the heater electrode 71, and heats and keeps the solid electrolyte forming the sensor element 101.

  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.

<Manufacturing process of sensor element>
Next, a process for manufacturing the sensor element 101 will be described in more detail.

  FIG. 2 is a diagram illustrating a flow of processing when the sensor element 101 is created. First, a green sheet containing an oxygen ion conductive solid electrolyte such as zirconia as a ceramic component is prepared (step 1). In the present embodiment, six green sheets are prepared corresponding to each layer. Since the sensor element 101 is obtained as a result of firing and shrinking the laminate of green sheets, the sensor element 101 is a green sheet so that the finally obtained sensor element 101 has a predetermined design dimension. Uses a firing shrinkage adjusted in advance within a predetermined range. In the present embodiment, description will be made on the assumption that the firing shrinkage rate of the laminate is set to about 10% to 30%. However, a specific target value of the firing shrinkage rate of each green sheet may be determined depending on which layer the green sheet is used for, and it is not necessarily the same for all the green sheets.

  Next, with respect to the green sheet corresponding to the layers constituting the internal space and the through hole 73, a penetrating portion corresponding to the internal space and the through hole 73 is formed by a punching process using a punching device (step 2).

  When a green sheet corresponding to each layer is prepared, pattern printing / drying processing is performed on each green sheet (step 3). For the printing process and drying process at this time, known printing means and drying means can be used.

  When the pattern printing is finished, a warp suppressing paste is applied to the upper surface of the green sheet corresponding to the second solid electrolyte layer 6 and the lower surface of the green sheet corresponding to the first substrate layer 1 (step 4). In other words, the warp-suppressing paste is applied to the surfaces that become the front and back surfaces when the laminate is configured. Preferably, the warp suppressing paste is applied in such a manner that the sensor element 101 covers the outer pump electrode 23 and other electrodes exposed to the outside.

  As a warp suppressing paste, any suitable paste can be used as long as it can form a sensor element 101 having a good shape by suppressing warping after firing. A preferred example is to use a paste prepared by mixing the mixed powder containing and the resin solution with a pot mill, a cracker or the like.

  In such a case, the mixed powder is preferably added with alumina as a main component and an inorganic compound (glass raw material component) as a subsidiary component (additive). More preferably, alumina is the main component, and silica stone powder, barium carbonate, calcium carbonate, magnesite powder, etc. are used as subcomponents, and the subcomponents are added so that the total amount is 3 wt% to 20 wt% of the total mixed powder. To do. More preferably, the subcomponents are added so that the total amount is 3 wt% or more and 15 wt% or less. If the subsidiary components are larger than 20% by weight in total, the generation of pinholes in the porous layer 90 formed after firing may increase, which is not preferable. In the case where the firing shrinkage rate of the laminate is determined within the above range, the specific proportion of each component in the mixed powder is 90% by weight or more of alumina when the entire mixed powder is 100% by weight. It is preferred that the content is 97% by weight or less, the silica powder is 10% by weight or less, the barium carbonate is 10% by weight or less, the calcium carbonate is 10% by weight or less, and the magnesite powder is 5% by weight or less. For example, 95% by weight of alumina, 2.6% by weight of silica powder, 1.6% by weight of barium carbonate, 1.8% by weight of calcium carbonate, and 0.6% by weight of magnesite powder. It is. Note that the porosity in the porous layer 90 can be adjusted by appropriately changing the degree of pulverization and specific surface area of the mixed powder.

  As the resin solution, a resin powder made of butyral resin, a solvent made of butyl carbitol, and a plasticizer are mixed, and a mixture of a dispersant and an acetone solvent is used. The resin powder is preferably used in an amount such that the dry resin powder is 1 to 35 g with respect to 100 g of the mixed powder, more preferably 20 to 25 g of dry resin powder with respect to 100 g of the mixed powder.

  The warp suppressing paste is applied so as to have a thickness of 5 μm or more and 20 μm or less. If the thickness is less than 5 μm, the effect of suppressing warpage cannot be obtained sufficiently, which is not preferable. On the other hand, if the coating thickness exceeds 20 μm, the produced porous body 90 may be peeled off or cracked, which is not preferable. More preferably, it is applied so as to have a thickness of 7 μm or more and 13 μm or less.

  Further, the warp suppressing paste is applied such that the application area is 68% or more with respect to the total area of the application surface. If the coating area is less than 68%, the effect of suppressing warpage cannot be obtained sufficiently, such being undesirable. More preferably, application is performed so that the application area is 75% or more with respect to the total area of the application surface.

  When the application of the warp suppressing paste is finished, printing / drying processing of an adhesive paste for laminating and adhering the green sheets corresponding to the respective layers is performed (step 5). Also for the printing process and drying process at this time, known printing means and drying means can be used.

  Subsequently, the green sheets to which the adhesive has been applied are stacked in a predetermined order, and are subjected to pressure bonding by applying predetermined temperature and pressure conditions to perform a pressure bonding process to form a single laminate (step 6). Specifically, it is performed by heating and pressurizing the entire stacking jig with a laminating machine such as a known hydraulic press machine. The pressure, temperature, and time for performing heating and pressurization depend on the laminating machine to be used, but appropriate conditions may be determined so that good lamination can be realized.

  When the laminated body is obtained as described above, subsequently, a plurality of portions of the laminated body are cut by a known cutting device, and each is cut into element bodies that are laminated bodies corresponding to the individual sensor elements 101 (steps). 7).

  When the cut element body is fired in an air atmosphere at a firing temperature of about 1200 to 1400 ° C. and a firing time of 1 hour or longer, the organic component evaporates, and the ceramic component constituting the element body portion The sensor element 101 is generated by the progress of the sintering and the sintering of the metal at the circuit pattern portion such as the electrode and the wiring (step 8).

<Effect of applying warp suppression paste>
By passing through the above processes, it is possible to obtain the sensor element 101 in which a predetermined design dimension is satisfied and the ratio of the warpage amount to the element thickness is suppressed within 10%. In the present embodiment, the warping amount is the lowest end portion when the lowermost end portion (both ends 102 and 103 in the longitudinal direction in FIG. 3) is supported by the table 400 as shown in FIG. This is the difference (L3−L4) between the distance L3 from the uppermost end 104 to the plate thickness L4 of the sensor element 101. In general, if the ratio of the amount of warpage to the element thickness is within 10%, the sensor element can be said to have a good shape when assembled to an external component such as a connector (not shown). The sensor element 101 obtained according to the form satisfies this requirement. That is, according to the manufacturing method according to the present embodiment, sensor element 101 in which warpage is satisfactorily suppressed is realized. This is the effect of applying the warp suppressing paste.

  In particular, when the ratio of additives in the mixed powder is 3% by weight or more and 15% by weight or less in total, when the application area of the warp suppression paste is 75% or more with respect to the total area of the coated surface, or warp suppression When the paste coating thickness is 7 μm or more and 13 μm or less, it is possible to obtain the sensor element 101 in which the warpage is further suppressed and the ratio of the warpage amount to the element thickness is suppressed to 2.5% or less.

  That is, by firing after applying the warp suppressing paste, each green sheet constituting the laminate (element body) shrinks while being affected by the firing shrinkage of the warp suppressing paste in the firing process. This means that the contraction behavior of each green sheet is regulated (or constrained) by the contraction of the warp suppressing paste.

  Specifically, by applying a warp-suppressing paste, the shrinkage of the green sheet, which is relatively easy to shrink when not applied, is inhibited during firing, or the shrinkage of the green sheet, which is relatively difficult to shrink. At least one of the promotion has occurred.

  Furthermore, the sensor element 101 after firing satisfies the design dimensions, and the warp suppressing paste itself applied to the surface of the laminate also shrinks to become the porous layer 90 during firing. Therefore, it can be said that the warp suppressing paste has not only a warp suppressing effect but also an effect of restraining (controlling) the firing shrinkage behavior of the entire laminated body (element body) by contracting itself. This means that the warp suppressing paste itself is prepared so as to shrink at a firing shrinkage rate substantially the same as the firing shrinkage rate of the laminate. In other words, in the present embodiment, a paste having a firing shrinkage rate substantially the same as the firing shrinkage rate of the laminate is prepared according to the above-described embodiment, and warping of the sensor element 101 is suppressed by using the paste. It can be said that.

  Further, when the porosity of the porous layer 90 formed in the fired sensor element 101 is 5% or more and 25% or less due to the shrinkage of the warp suppressing paste by firing, The ratio of warpage is within 10%. This means that the warpage in the sensor element 101 is suppressed by controlling the porosity of the porous layer 90 in the range of 5% to 25%. In other words, it can be said that the sensor element 101 including the porous layer 90 having the porosity after firing realizes the above-described control of the shrinkage behavior and the warpage suppression of the sensor element 101 by the warp suppression paste. . In particular, when the porosity of the porous layer 90 is controlled in the range of 10% or more and 20% or less, the sensor element 101 in which the ratio of the warpage amount to the element thickness is suppressed to 2.5% or less is realized. The

  As described above, according to the present embodiment, it is possible to obtain a good sensor element in which the warpage is suppressed by applying the warpage suppressing paste to the front and back surfaces of the laminate and performing the firing. That is, by adding a simple and low-cost process of applying a warp suppressing paste to a conventional sensor element manufacturing process, a sensor element with a warp suppressed as compared with the conventional method can be obtained.

  Although the description so far has been made on a sensor element made of oxygen ion conductive solid electrolyte ceramics, the effect of applying the warp suppressing paste is the same as the green sheet process of the sensor element. It can also be obtained in other multilayer ceramic devices manufactured by using them. That is, the method of the present invention can be similarly applied to multilayer ceramic devices in general.

<Modification>
In the above-described embodiment, the case where the warp suppressing paste is applied to the front and back surfaces of the laminate has been described. However, the application of the present invention is not limited to this, and the paste is applied to either the front or back surface of the laminate. It is also possible to use this mode.

  Moreover, in the above-described embodiment, the case where the warp suppressing paste is applied after the electrode pattern or the like is printed on the ceramic green sheet has been described. Instead, the ceramic green sheet is laminated on the front and back surfaces of the laminated body. The aspect which apply | coats a curvature suppression paste may be sufficient, and the aspect which apply | coats the curvature suppression paste with respect to each element body after cutting out this laminated body to an element body may be sufficient.

  Sensor elements were produced in which the porosity of the porous layer, the ratio of the additive in the mixed powder in the warp suppressing paste, the coating area, and the coating thickness were varied, and the warp inspection was performed for each.

  Specifically, in addition to producing one type of sensor element that does not have a porous layer (Experimental Example 1), five levels of samples that differ only in porosity by changing the pulverization degree and specific surface area of the mixed powder (experimental) Example 2 to Experiment 6), 5 levels of samples with different additive ratios only (Experimental Examples 7 to 11), 4 samples with different application areas only (Experimental Examples 12 to 15), Five samples (Experimental Example 16 to Experimental Example 20) with different coating thicknesses were prepared. The porosity was measured with a mercury porosimeter. The application area of the warp suppressing paste was set as the specifications of the plate making used for application. The coating thickness of the warp suppressing paste was measured with a dial gauge. And the amount of curvature and element thickness of each sensor element were calculated | required using the laser measuring device.

  FIG. 4 is a diagram showing the conditions for each sample and the results of the warpage inspection. In FIG. 4, the result of the warpage inspection is shown as a ratio of the warpage amount to the element thickness of the sensor element. As shown in FIG. 4, in Experimental Example 1, the warping amount of the sensor element reaches 22% of the element thickness, whereas the porosity is 5% or more and 25% or less, and the ratio of the additive is 3% by weight or more. It was confirmed that when the coating area was 20% by weight or less, the coating area was 68% or more, or the coating thickness was 5 μm or more and 20 μm or less, the warping amount of the sensor element was suppressed within 5% of the element thickness.

  Furthermore, as a result of comparing Experimental Example 2 to Experimental Example 6 in which only the porosity was changed, as a result of comparing Experimental Example 7 to Experimental Example 11 in which only the ratio of the additive was changed, only the application area of the warp suppressing paste was changed. When the porosity is 10% or more and 20% or less from the result of comparing Experimental Example 12 to Experimental Example 15 and the result of comparing Experimental Example 16 to Experimental Example 20 in which only the coating thickness of the warp suppressing paste is different When the ratio of the additive is 3% by weight or more and 15% by weight or less, when the coating area is 75% or more, or when the coating thickness is 7 μm or more and 13 μm or less, the warping amount of the sensor element It was confirmed that is suppressed to 2.5% or less of the element thickness.

DESCRIPTION OF SYMBOLS 1 1st board | substrate layer 2 2nd board | substrate layer 3 3rd board | substrate layer 4 1st solid electrolyte layer 5 Spacer layer 6 2nd solid electrolyte layer 90 Porous layer 100 Gas sensor 101 Sensor element

Claims (7)

A method for producing a ceramic device by firing a laminate of a plurality of ceramic green sheets,
a) applying only a ceramic green sheet serving as a front surface and a back surface of the laminate, a paste containing alumina as a main component and having a restraining ability for firing shrinkage behavior of the laminate during firing;
b) firing the laminate to which the paste is applied to obtain a ceramic device by firing and shrinking the laminate at a predetermined shrinkage rate under the constraint of firing shrinkage behavior of the paste;
Equipped with a,
In the step b), after obtaining the laminate by adhering the ceramic green sheet coated with the paste in the step a) and another ceramic green sheet with an adhesive paste, the laminate is obtained. Bake,
A method for producing a ceramic device. A method for producing a ceramic device according to claim 1,
A method for producing a ceramic device, wherein the paste application area ratio on the ceramic green sheets to be the front and back surfaces of the laminate in step a) is 68% or more . A method for manufacturing a ceramic device according to claim 1 or 2,
A method for producing a ceramic device, wherein a thickness of the paste applied to the ceramic green sheets to be the front and back surfaces of the laminate in step a) is 5 μm or more and 20 μm or less . A method for manufacturing a ceramic device according to any one of claims 1 to 3,
The method for producing a ceramic device, wherein a ratio of the additive in the paste in the step a) is 3% by weight or more and 20% by weight or less . A method for producing a ceramic device according to any one of claims 1 to 4,
The method for producing a ceramic device, wherein the ceramic device obtained in the step b) includes a porous layer having a porosity of 5% or more and 25% or less on a front surface and a back surface . A method for producing a ceramic device according to any one of claims 1 to 5,
A ceramic device manufacturing method, wherein the ceramic device is a sensor element made of oxygen ion conductive solid electrolyte ceramics . A ceramic device manufactured by the manufacturing method according to claim 1.

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