JP2005283285A - Oxygen concentration detection sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen concentration detection sensor constituted so that the insulating properties are sufficiently held, a leak current or the like is generated, a crack or the like is not formed in the vicinity of a heater, the concentration of oxygen can be measured with high measuring precision and durability is excellent. <P>SOLUTION: The oxygen concentration detection sensor 10 is constituted of an inspection layer 20 having a gas introducing opening 22 for introducing a gas to be measured containing oxygen, the solid electrolyte plate having an oxygen ion conductivity formed on the inspection layer 20, the undersurface electrode 18 formed to the undersurface thereof, and the upper surface electrode 13 formed on the upper surface thereof and an oxygen pump layer 11 having an oxygen pump function and the heater layer constituted of at least a heater 53 and an insulating layer in which the heater 53 is embedded. The insulating layer 50 is constituted so as to contain the insulating layer in which at least the heater 53 and the insulating layer in which the heater 53 is embedded. The voids of the insulating layer constituting the heater layer 50 is 5% or less and the heater 53 constituted of 90 pts.wt. or above of a metal and at least one of a component selected from a group consisting of 10 pts.wt. of below alumina magnesia and a spinel. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an oxygen concentration detection sensor used when measuring an oxygen concentration in a gas to be measured.

As a gas sensor element used for a gas sensor for detecting a component to be detected in a gas to be measured, such as an oxygen sensor or a NOx sensor, a stacked gas sensor element formed by stacking a plurality of solid electrolyte layers is known.

Such a stacked gas sensor element mainly includes a solid electrolyte plate having electrodes formed on the front and back sides thereof and a heater, and the temperature of the sensor element is raised to a predetermined temperature by heat generated from the heater. The oxygen concentration can be measured based on the electromotive force of the concentration cell in the region.

Patent Documents 1, 2 and the like are known as conventional techniques related to such a stacked gas sensor element.
Patent Document 1 discloses a basic configuration of a stacked gas sensor element including a heating element, and Patent Document 2 discloses a porosity of an insulating layer made of ceramic in which a heater is embedded in a range of 5 to 50%. Thus, there is described a multilayer gas sensor element capable of preventing the occurrence of cracks, disconnection of a resistance heating element, and the like even when a larger voltage is applied than before.

JP-A-55-116248 JP 2002-71628 A

However, as described in Patent Document 2, when the porosity of the insulating layer in which the heater is embedded is set in the range of 5 to 50%, the ratio of the gas present in the insulator increases, In this case, a leak current or the like is easily generated via gas, and insulation near the heater may not be completely maintained.

Therefore, in order to increase the insulating property of the insulating layer and prevent the occurrence of leakage current, etc., it has been studied to use an insulating layer with a porosity of 5% or less.

However, if the denseness of the insulating layer made of ceramic is improved, the rigidity of the insulating layer also increases. Therefore, when a green sheet containing a solid electrolyte, a paste layer serving as a heater is laminated and fired, such as a green sheet embedded in a sheet containing an insulating powder such as alumina, the insulating layer, particularly in the vicinity where the heater is formed There was a problem that cracks and the like occurred and reliability was lowered.

The present invention has been made in view of such problems, and the insulation of the heater is sufficiently maintained, no leakage current or the like occurs, cracks or the like do not occur in the vicinity of the heater, and high measurement accuracy is achieved. An object of the present invention is to provide an oxygen concentration detection sensor excellent in durability that can measure the oxygen concentration.

An oxygen concentration detection sensor according to the present invention includes a test layer having a gas introduction opening for introducing a gas to be measured containing oxygen, a solid electrolyte plate formed on the test layer, and having oxygen ion conductivity. The lower surface electrode formed on the lower surface of the solid electrolyte plate and the upper surface electrode formed on the upper surface of the solid electrolyte plate, an oxygen pump layer having an oxygen pump function, and at least a heater and the heater are embedded An oxygen concentration detection sensor comprising a heater layer configured to include an insulating layer,
The insulating layer constituting the heater layer has a porosity of 5% or less,
The heater is composed of 90 parts by weight or more of metal and 10 parts by weight or less of at least one selected from the group consisting of alumina, magnesia and spinel.

In the oxygen concentration detection sensor of the present invention, the metal constituting the heater is preferably made of Pt or Pt—Au.
The heater is composed of 90 parts by weight or more of Pt and 10 parts by weight or less of alumina, and the average particle diameter of the alumina is preferably the same as or smaller than the average particle diameter of the Pt.
In the oxygen concentration detection sensor of the present invention, when the total thickness of the heater and the insulating layer is A, and the thickness of the insulating layer is B,
It is desirable that the heater and the insulating layer satisfy the relationship of the following formula (1).
1.0 <A / B ≦ 1.2 (1)

Conventionally, since the heater constituting the oxygen concentration detection sensor is formed only of metal, the heater is compared with the ceramic constituting the insulating layer in which the heater is embedded in the firing process at the time of manufacturing the oxygen concentration detection sensor. Then, shrinkage (sintering) starts in a lower temperature region, and in the temperature region where ceramic shrinkage (sintering) starts, the shrinkage has already finished, and the insulating layer shrinks around the heater where shrinkage has finished. Therefore, in the heater layer after sintering, a large stress is generated between the heater and the insulating layer, which may cause cracks in the insulating layer or breakage of the heater.

However, in the oxygen concentration detection sensor of the present invention, the porosity of the insulating layer constituting the heater layer is 5% or less, and the heater is made of 90 parts by weight or more of metal and 10 parts by weight or less of alumina, magnesia and spinel. Since the temperature region where the heater shrinks (sinters) overlaps with the temperature region where the insulating layer shrinks (sinters), the insulating layer shrinks when the insulating layer shrinks. A certain amount of deformation is possible depending on the case. Therefore, in the heater layer after sintering, no great stress is generated between the heater and the insulating layer, and no crack is generated in the insulating layer and no breakage occurs in the heater.
In addition, the porosity of the insulating layer is 5% or less and it is relatively dense and the proportion of the air layer is small. Therefore, even if the temperature is high, the insulation of the heater is sufficiently maintained, leak current does not occur, and high measurement is possible. It becomes an oxygen concentration detection sensor excellent in durability that can measure the oxygen concentration with high accuracy.

Regarding problems such as the occurrence of cracks, for example, when alumina is used as the material of the insulating layer, Pt is used as the material of the heater, and ceramics such as alumina are not blended with Pt, when the temperature is increased, Pt is about 500 ° C. Shrinkage starts from 1 and the shrinkage is completed at around 1100 ° C. Thereafter, even if the temperature is raised to around 1770 ° C., which is the melting point of Pt, it hardly shrinks.
On the other hand, the shrinkage of alumina starts at 1100 ° C., and the shrinkage is completed around 1390 ° C.
When ordinary paste is used, the shrinkage rate of Pt is 20% and the shrinkage rate of alumina is 19%, and the shrinkage rate of both is not much different, but the shrinkage of Pt is completed near the temperature at which alumina starts shrinking. Conversely, alumina does not shrink in the temperature range where Pt begins to shrink.
However, when using a heater with Pt mixed with alumina, the mixed alumina expands the temperature range in which it shrinks, and the heater shrinks even in the temperature range above 1100 ° C, causing cracks in the insulating layer and the heater. Can be prevented from occurring.

An oxygen concentration detection sensor according to the present invention includes a test layer having a gas introduction opening for introducing a gas to be measured containing oxygen, a solid electrolyte plate formed on the test layer, and having oxygen ion conductivity. The lower surface electrode formed on the lower surface of the solid electrolyte plate and the upper surface electrode formed on the upper surface of the solid electrolyte plate, an oxygen pump layer having an oxygen pump function, and at least a heater and the heater are embedded An oxygen concentration detection sensor comprising a heater layer configured to include an insulating layer,
The insulating layer constituting the heater layer has a porosity of 5% or less, and the heater is at least one selected from the group consisting of 90 parts by weight of metal and 10 parts by weight of alumina, magnesia, and spinel. It is composed of seeds.

The blending ratio of the metal and at least one selected from the group consisting of alumina, magnesia and spinel (hereinafter referred to as ceramic such as alumina) is 90 parts by weight or more for metal and 10 parts by weight or less for ceramic such as alumina. is there. The spinel is a double oxide (Al ₂ O ₃ .MgO) mainly composed of alumina and magnesia.

When the mixing ratio of ceramic such as alumina in the heater exceeds 10 wt%, the shrinkage ratio of the heater is reduced and the shrinkage difference from the ceramic material constituting the insulating layer is increased.

The mixing ratio of the metal and ceramic such as alumina in the heater is desirably 95 parts by weight or more for metal and 5 parts by weight or less for ceramic such as alumina. This is because the shrinkage temperature region can be enlarged and the shrinkage rate of both can be made closer by setting the above range.

The metal constituting the heater is preferably made of Pt or Pt—Au. This is because the melting point is high and the shrinkage start temperature can be kept high to some extent.

The heater is composed of 90 parts by weight or more of Pt and 10 parts by weight or less of alumina, and the average particle diameter of the alumina is preferably the same as or smaller than the average particle diameter of the Pt.
When the average particle size of alumina is larger than the average particle size of Pt (for example, Pt particle size: 0.5 μm, alumina particle size: 1.0 μm or more), the volume of alumina is smaller than the volume of Pt. Thus, there are many portions where alumina does not exist between the Pt and Pt particles, and the shrinkage start temperature of Pt cannot be sufficiently delayed. For this reason, stress is easily generated in the shrinking process of both materials, and cracks are easily generated in the heater and the insulating layer.
The average particle diameter of alumina is more preferably ½ or less of the average particle diameter of Pt.

When the total thickness of the heater and the insulating layer is A, and the thickness of the insulating layer is B,
It is desirable that the heater and the insulating layer satisfy the relationship of the following formula (1).
1.0 <A / B ≦ 1.2 (1)

By setting the thickness relationship between the heater and the insulating layer so as to satisfy the expression (1), it is possible to prevent the occurrence of cracks and the like even for a porous insulating layer with increased rigidity. it can.
In the above formula (1), when A / B ≦ 1.0, the insulating layer portion becomes thick, so the amount of stress generated inside the insulating layer increases, and the insulating layer with increased rigidity This stress cannot be relaxed sufficiently.

On the contrary, when A / B> 1.2, the ratio of the thickness of the heater increases, and the insulation layer shrinks in the region where the heater does not shrink, so that the insulation layer and the surrounding layers are A void is likely to be formed, and the stress generated in the void is also applied to the insulating layer, and the stress cannot be sufficiently relaxed, and cracks and the like are likely to occur.
Particularly desirable is a range of 1.03 ≦ A / B ≦ 1.10. Within this range, the amount of stress generated does not increase, the stress is easily relaxed inside the insulating layer, and cracks and the like are eliminated.

FIG. 1 is an exploded perspective view schematically showing an example of the oxygen concentration detection sensor of the present invention, and FIG. 2 is a cross-sectional view schematically showing a heater layer.

As shown in FIG. 1, in the oxygen concentration detection sensor 10, a heater layer 50 having a heater 53 is formed at the bottom, and an air duct layer 40 and a reference layer 30 having electrodes above and below are sequentially formed thereon. An inspection layer 20 in which an opening 22 for gas introduction serving as an inspection room is formed, and an oxygen pump layer 11 having electrodes on the upper and lower sides are provided.

Although the magnitude | size of this oxygen concentration detection sensor 10 is not specifically limited, For example, the range of width 3-10mm, length 35-70mm, and thickness 1.0-5mm is preferable.

As shown in FIG. 2, the heater layer 50 constituting the oxygen concentration detection sensor 10 is composed of two materials of a solid electrolyte and alumina ceramic, and the heater upper layer 51 above the portion where the heater 53 is formed. The insulating layer 54a and the insulating layer 54b formed above the heater lower layer 52 are made of alumina ceramic, and the solid electrolyte layer 55 is formed under the insulating layer 54b.

That is, in order to prevent the occurrence of a leakage current, the heater 53 is formed in a mode of being sandwiched between insulating layers 54a and 54b made of alumina ceramic or the like having a porosity of 5% or less, and underneath it is heated. A solid electrolyte layer 55 for matching the expansion coefficient and the like is formed. The material of the insulating layers 54a and 54b is not particularly limited, but alumina is preferable. It is because it is excellent in insulation.

The heater 53 is composed of 90 parts by weight or more of a metal and 10 parts by weight or less of a ceramic such as alumina. With such a structure, the insulating layer cracks or the heater It is possible to prevent disconnection. In particular, the ratio of the metal constituting the heater 53 and the ceramic such as alumina is preferably 95 parts by weight or more for metal and 5 parts by weight or less for ceramics such as alumina.

In addition, when the heater layer 50 and the other layer mainly formed of the solid electrolyte are integrally sintered, the solid electrolyte plate and the insulating layer 54 (54a, 54b) are caused by a difference in contraction rate or a difference in thermal expansion rate. Cracks may occur, but between them, as a spacer, a mixed layer of a solid electrolyte such as a porous body or a composite of zirconia and alumina and an insulator is inserted to ensure cracks and the like. Can be prevented.

The heater 53 includes a heat generating portion 53b and a lead portion 53a. The lead portion 53a includes a through hole 90 and heater terminals 530a and 530b.

As a metal which comprises the heater 53, metals, such as Pt and Pd, and alloys, such as Pt-Ag and Pt-Au, are mentioned, for example. Since these metals have heat resistance and are less likely to completely melt and flow out even at a high temperature of around 1400 ° C. during firing, they are preferably used as the metal constituting the heater. Pt is preferable as the metal material constituting the heater 53, and alumina is preferable as the ceramic such as alumina.

The average particle size of alumina is desirably the same as or smaller than the average particle size of Pt. The average particle size of Pt is preferably 0.5 to 2.0 μm, and the average particle size of alumina is the same as or smaller than the average particle size of Pt, and preferably 0.2 to 0.5 μm. If the average particle diameter of alumina exceeds 2.0 μm, the frequency of occurrence of cracks and breaks in the insulating layer increases, whereas if it is less than 0.5 μm, the particles tend to aggregate, and as a result, the aggregated particles The diameter may exceed 20 μm.
The average particle diameter of alumina is more preferably ½ or less of the average particle diameter of Pt.
As a specific example, there is a case where the average particle diameter of Pt is 0.5 μm and the average particle diameter of alumina is 0.2 μm, which is 1/2 or less thereof.

When forming the heater, a paste made of the above-described metal or alloy can be used. In addition, a chemical method such as plating may be used, or a physical method such as vapor deposition or sputtering is used. May be. The same applies when other electrodes and lead portions are formed.

The diameter of the through hole is desirably 250 to 350 μm. Further, it is desirable that the through hole is filled with metal as shown in FIG. The metal layer constituting the through hole preferably has a ratio of at least one selected from the group consisting of alumina, magnesia, and spinel more than other lead portions, heat generating portions, and the like. That is, it is desirable that the through hole is composed of 80 parts by weight or more of metal and 20 parts by weight or less of alumina or the like.

As shown in FIG. 2, it is desirable that an insulating layer 54 b having a predetermined thickness is interposed between the solid electrolyte layer 55 and the through hole 90.
When the solid electrolyte layer 55 and the through hole 90 come into contact with each other at the through hole 90 portion, the applied voltage for the oxygen pump is picked up at the through hole 90 portion, or the current for the heater 53 flows out to the solid electrolyte layer 55, causing noise. This is because it causes the occurrence.

On the heater layer 50 having the above-described configuration, an air duct layer 40 made of a solid electrolyte plate 41 in which an elongated notch 42 for taking in air is formed is provided.

A reference layer 30 is provided on the air duct layer 40.
The reference layer 30 includes a solid electrolyte plate 31 having oxygen ion conductivity, a reference layer lower surface electrode 34 formed on the lower surface of the solid electrolyte plate 31, and a reference layer upper surface electrode 32 formed on the upper surface of the solid electrolyte plate 31. In addition, the reference layer lower surface electrode 34 is exposed at a deep part of the opening 42 of the air duct layer 40 formed below, and can come into contact with the atmosphere.

The reference layer upper surface electrode 32 is exposed to a gas introduction opening 22 (inspection chamber) formed in the inspection layer 20 which is an upper layer, and the concentration is adjusted so that the exhaust gas has a predetermined reference oxygen concentration. It comes in contact with the gas. The gas whose concentration is adjusted so that the exhaust gas has a predetermined reference oxygen concentration will be described in detail later.

In the reference layer 30, as described above, the solid electrolyte plate 31 is sandwiched between the reference layer lower surface electrode 34 in contact with the atmosphere and the reference layer upper surface electrode 32 in contact with a gas having a predetermined oxygen concentration serving as a reference. Since the concentration cell is formed between the atmosphere and the gas having the reference oxygen concentration, an electromotive force is generated during that time. Therefore, this electromotive force is measured, and the oxygen concentration in the laboratory is adjusted so that the electromotive force becomes a predetermined value. Examples of the material of the reference layer lower surface electrode 34 and the reference layer upper surface electrode 32 include Pt.

An inspection layer 20 is provided on the reference layer 30 configured as described above.
The inspection layer 20 is mainly composed of a solid electrolyte plate 21. In the drawing, a gas introduction opening 22 as an inspection room is formed near the right end, and an exhaust gas is formed on the right side of the opening. A porous gas diffusion layer 23 through which the gas passes is provided. The gas diffusion layer 23 limits the diffusion of the gas to be measured so that the gas to be measured existing outside the sensor body and the gas to be measured existing in the gas introduction opening 22 do not immediately reach an equilibrium state. Play a role. Therefore, the concentration of the gas in the gas introduction opening 22 is adjusted to a predetermined reference oxygen concentration by a mechanism described later, and a stable output value can be obtained.

An oxygen pump layer 11 is provided on the inspection layer 20 having the above configuration.
The oxygen pump layer 11 includes a solid electrolyte plate 12 having oxygen ion conductivity, a pump layer lower surface electrode 18 formed on the lower surface of the solid electrolyte plate 12, and a pump layer upper surface electrode 13 formed on the upper surface of the solid electrolyte plate 12. The protective layer 15 protects the electrode portion 13 a of the pump layer upper surface electrode 13. The lead portion 13 b of the pump layer upper surface electrode 13 is formed on the upper surface of the solid electrolyte plate 12 with the insulating layer 14 interposed therebetween.

The oxygen pump layer 11 literally has a function of pumping / pumping oxygen, and by applying a voltage between the pump layer lower surface electrode 18 and the pump layer upper surface electrode 13, the exhaust gas taken in is predetermined. Thus, oxygen is pumped into the examination room (gas introduction opening 22) or oxygen in the examination room (gas introduction opening 22) is pumped out so that the reference oxygen concentration becomes the same. For example, when an electric current is applied so that the pump layer lower surface electrode 18 is a negative electrode and the pump layer upper surface electrode 13 is a positive electrode, oxygen ions are conducted from the negative electrode to the positive electrode, so that oxygen is pumped out from the laboratory. When current flows with the polarity reversed, oxygen is pumped into the examination room.
The predetermined reference oxygen concentration refers to the oxygen concentration in the exhaust gas when the combustion of the engine is performed at the theoretical air ratio (optimum air ratio).

That is, the limit current value generated by the voltage applied in the oxygen pump layer 11 shows a deviation from the theoretical ratio. For example, in the vehicle control device that has received the current signal of the oxygen pump, this current value The fuel injection amount of the engine is adjusted so that becomes a specific value.

The pump layer lower surface electrode 18 is a material having a high ability to detect oxygen concentration and decompose nitrogen oxides, for example, a material mainly containing one or more of platinum, rhodium, and platinum-rhodium alloy. It is desirable that When these materials are used, they do not melt even in the temperature range of 1000 ° C. On the other hand, the upper surface electrode may be made of any metal material. Examples of the metal material include platinum.

Further, since the solid electrolyte plates 12, 21, and 31 constituting the oxygen concentration detection sensor 10 function at 600 ° C. or higher, the temperature near the electrodes of the oxygen pump layer 11 and the reference layer can be increased by providing the heater layer 50. The temperature is controlled so as to be 600 ° C. or higher. The temperature in the vicinity of the electrode is more preferably 700 to 800 ° C.

Examples of the solid electrolyte include zirconia (YSZ) using yttria as a dopant, but the solid electrolyte is not limited to this and may be any one having oxygen ion conductivity. Although the thickness of each solid electrolyte board can be set, for example in the range of 0.1-1 mm, As for the thickness of each solid electrolyte, 0.2-0.6 mm is more preferable.

In the oxygen concentration detection sensor of the present invention, the electrodes provided above and below the oxygen pump layer are connected to each other so that a voltage can be applied by the I _P1 drive circuit via the lead portions. Also,
And vertically electrodes provided in the reference layer reference electrode and the oxygen pump layer provided on the upper and lower surfaces of the can are connected so as to be able to detect a potential difference between the electrodes by V _S detection circuit via the lead portion, respectively Yes.

Then, the potential difference (voltage) caused by the difference between the oxygen concentration in the atmosphere and the oxygen concentration in the exhaust gas measured by the reference electrode is compared with the reference potential difference (for example, 450 mV) in the theoretical air ratio, Oxygen is moved by applying a voltage to the electrodes provided above and below the oxygen pump layer so that the difference becomes zero.

Then, a signal of a limit current value generated by the voltage applied to the oxygen pump layer is transmitted to the control device or the like, and the air-fuel ratio is divided from the current value so that the air-fuel ratio becomes a specific value. The fuel injection amount of the engine is adjusted.

Next, a method for manufacturing the oxygen concentration detection sensor of the present invention will be described.
(1) Production of sheet to be solid electrolyte plate A binder and a solvent are added to the powder to be a solid electrolyte plate to prepare a paste for the solid electrolyte plate, and a green sheet is produced using a doctor blade method. Although the powder is not particularly limited as the solid electrolyte plate, for example, a main component of zirconia (ZrO _2), yttria other, powders containing alumina or the like. The powder that becomes the solid electrolyte plate may be a powder having a predetermined composition by calcination or the like, or may be a mixed powder containing these components and having a predetermined composition after firing. Further, the material of the solid electrolyte plate is not limited to the above composition, and any material having oxygen ion conductivity may be used.
The thickness of the green sheet is set to be within a range of 0.1 to 1 mm after firing, for example.

(2) Creation of a sheet to be an oxygen pump layer Using the green sheet produced in the step (1), a mask in which an opening in the shape of the insulating layer 14 is formed is placed, and an insulating ceramic such as alumina paste is included. Using the paste, a paste layer to be an insulating layer is formed, dried and cured. However, the insulating layer is not an essential layer, and a step of forming a paste layer that becomes an insulating layer may be omitted.

Next, drilling is performed on the portions of the green sheet that have been subjected to the above-described steps to become the ground terminal 16 and the reference terminal 17 so that the opening diameter after firing is 250 to 350 μm to form through holes (through holes). Then, it is filled with Pt paste or the like, dried and cured.
A mask having openings in the shape of the ground terminal 16 and the reference terminal 17 is placed, and a conductor paste such as a Pt paste is printed to form a conductor paste layer that becomes the ground terminal 16 and the reference terminal 17, and is dried and cured. When using the Pt paste, for example, a Pt particle having a particle diameter of 0.5 μm, a binder such as ethyl cellulose, and an acrylic solvent can be kneaded and adjusted to a predetermined viscosity.
In addition, formation of conductor layers, such as an electrode and a lead part, can be performed by sputtering, vapor deposition, and plating besides using a paste. The same applies to the following electrodes, lead portions, heating elements, and the like.

Next, a mask having an opening in the shape of a pump upper surface electrode including a lead portion is placed, and a conductor paste such as a Pt paste is printed to form a conductor paste layer that becomes a pump upper surface electrode, and is dried and cured. When using the Pt paste, for example, a Pt particle having a particle size of 0.5 μm and an ethyl cellulose / acrylic solvent kneaded and adjusted to a predetermined viscosity can be used.

Thereafter, printing is performed on the opposite surface on which the paste layer for the pump upper surface electrode is formed using a conductive paste such as a Pt paste to form a paste layer for the pump lower surface electrode including the lead portion. In order to form an electrode having a high ability to reduce nitrogen oxides, such as a pump bottom electrode, a paste containing one or more of Pt, rhodium, and an alloy of Pt and rhodium as a main component is used. desirable.

When using a platinum (Pt) -rhodium (Rh) paste, for example, Pt particles having a particle size of 0.5 μm and Rh particles having a particle size of 0.5 μm are blended at a ratio of 5: 1, and a binder such as ethyl cellulose is used. And an acrylic solvent may be added and kneaded to adjust the viscosity to 143 Pa · S (measured with a B-type viscometer at 10 rpm).
It is desirable to form a layer serving as a protective layer on the paste layer serving as the pump upper surface electrode.

(3) Production of sheet to be inspected layer An opening is formed in a region corresponding to the gas introduction opening of the green sheet obtained in the step (1) by using a drill or a laser. Also, a through hole is formed by a drill and filled with a Pt paste or the like.
(4) Production of Sheet as Reference Layer Using the green sheet obtained in the step (1), first, a through hole is formed by a drill and filled with a Pt paste or the like. Next, a conductor paste such as the Pt paste is printed on the upper and lower surfaces of the sheet to form a layer that becomes an electrode for the reference layer. When using a Pt paste, the same paste as that used for the production of the oxygen pump layer can be used.

(5) Production of sheet to be air duct layer A region corresponding to the air duct of the green sheet obtained in the step (1) is cut out using a laser or a drill to form a notch to be an air duct.

(6) Preparation of sheet to be a heater layer Using the green sheet obtained in the step (1), first, the sheet is subjected to drilling so that the opening diameter after firing becomes 250 to 350 μm, and the through hole is formed. (Through hole) is formed.
Next, a paste containing insulating ceramic powder such as alumina powder is used to form a paste layer of insulating ceramic powder to be an insulating layer on the front and back of the green sheet obtained in the step (1), and through holes are formed. Then, a paste layer serving as an insulating layer is formed on the inner wall surface layer of the through hole, and dried and cured.

The particle size, binder, solvent and the like of powder such as alumina ceramic contained in the paste layer are set so that the porosity of the insulating layer after firing at a predetermined temperature is 5% or less.

Next, a paste containing a heater material composed of 90 parts by weight or more of a metal such as Pt and 10 parts by weight or less of a ceramic such as alumina is filled in a through hole, dried and cured, and then screen printed or the like. A heater pattern paste layer is formed, dried and cured. At that time, the pattern to be printed is reversed from that printed on the heater. Further, a layer to be an insulating layer is formed thereon.
Regarding the relationship between the thickness of the fired heater and the insulating layer, assuming that the total thickness of the fired heater and the insulating layer is A and the thickness of the insulating layer is B, the heater and the insulating layer are as follows: It is desirable to satisfy the relationship of (1).
1.0 <A / B ≦ 1.2 (1)
Accordingly, the thickness of the paste layer of the heater pattern and the thickness of the paste layer serving as the insulating layer are adjusted so as to satisfy the relationship of the above formula (1).

(7) Firing First, a porous material made of alumina or the like is embedded in a portion that becomes a gas diffusion layer of a sheet that becomes an inspection layer manufactured by the above-described method. Thereafter, the sheets are laminated in the order of the oxygen pump layer, the inspection layer, the reference layer, the air duct layer, and the heater layer. In addition, between each sheet | seat, the adhesive sheet which consists of insulating resin for adhesion | attachment may be inserted, and each sheet | seat may be affixed through this adhesive sheet. The adhesive sheet is a sheet mainly composed of a solid electrolyte powder such as zirconia and a binder of a thermoplastic resin such as terephthalic acid and sebacic acid, and other components such as a solvent and additives.
After degreasing the laminate thus produced, it is fired at 1400-1500 ° C. to obtain a sintered body for an oxygen concentration detection sensor.

(8) External shape processing The end surface of the obtained sintered body is mechanically polished so that the diffusion layer is exposed to the outside air, and the shape (for example, including length adjustment) is adjusted, thereby providing an oxygen concentration detection sensor. Can be obtained.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited only to these examples.

(Example 1)
(1) Production of Green Sheet to be Solid Electrolyte Plate 90.04 wt% Zirconia (ZrO ₂ ), 9.96 wt% Yttria (Y ₂ O ₃ ), 2.68% Alumina (Al ₂ O ₃ ) A solid electrolyte plate paste is prepared by blending 80 parts by weight of ethyl cellulose and 20 parts by weight of butyl carbitol with 100 parts by weight of a solid electrolyte powder composed of a small amount of iron oxide, titanium oxide, etc., and a doctor blade method Were used to prepare a sheet material A having a width of 15 mm, a length of 94 mm, and a thickness of 0.25 mm, and a sheet material B having a width of 15 mm, a length of 94 mm, and a thickness of 0.5 mm.

(2) Preparation of a sheet to be an oxygen pump layer First, the sheet material B prepared in (1) was used to place a mask in which an opening in the shape of the insulating layer 14 was formed, and 45 parts by weight of alumina powder (average Using an alumina paste made of 40 parts by weight ethyl cellulose (binder) and 15 parts by weight butyl carbitol (solvent), an alumina paste layer to be the insulating layer 14 is formed, dried and cured. It was.

Next, the sheet material B on which the alumina paste layer to be the insulating layer 14 is formed is drilled on the portions to be the ground terminal 16 and the reference terminal 17 using a drill, and a through hole (through-hole with an opening diameter of 350 μm) is formed. Hole) was formed and filled with Pt paste A.
Next, a mask having openings in the shape of the ground terminal 16 and the reference terminal 17 is placed, and Pt paste A is printed to form a Pt paste layer that becomes the ground terminal 16 and the reference terminal 17, and is dried and cured. . The Pt paste A used was prepared by kneading Pt particles having a particle size of 0.5 μm and an ethyl cellulose / acrylic solvent and adjusting the viscosity to 143 Pa · S (measured at a B-type viscometer at 10 rpm).

Next, a mask having an opening in the shape of the pump upper surface electrode was placed, and a Pt paste was printed to form a Pt paste layer to be the pump upper surface electrode, which was dried and cured. The Pt paste used was prepared by kneading Pt particles having a particle size of 0.5 μm and an ethyl cellulose / acrylic solvent to adjust the viscosity to 143 Pa · S (measured at a B-type viscometer at 10 rpm).
Thereafter, printing was performed on the opposite surface on which the paste layer for the pump upper surface electrode was formed using the Pt paste. Further, a layer made of zirconia paste serving as a protective layer was formed on the Pt paste layer serving as the pump upper surface electrode.

(3) Using a drill for producing a sheet to be an inspection layer, an opening was formed in a region corresponding to the gas introduction opening of the sheet material A. Further, a through hole having an opening diameter of 350 μm was formed by a drill and filled with Pt paste A.
(4) Preparation of sheet to be a reference layer Using the sheet material A, first, a through hole having an opening diameter of 350 μm is formed by a drill and filled with a Pt paste or the like. Next, an electrode for a reference layer was formed by printing a Pt paste on the upper and lower surfaces of the sheet. As the Pt paste, the same paste as that used for producing the electrode paste layer of the oxygen pump layer was used.

(5) Production of sheet to be an air duct layer A region corresponding to the air duct of the sheet material A was cut out using a laser to form a notch to be an air duct.

(6) Preparation of sheet to be a heater layer Using the sheet material B, first, a through hole having an opening diameter of 350 μm was formed by drilling the sheet.
Next, the front and back of the sheet B are insulated using an alumina paste composed of 45% by weight alumina powder (average particle size 0.2 μm), 40% by weight ethyl cellulose (binder) and 15 parts by weight butyl carbitol (solvent). An alumina paste layer to be a layer was formed and sucked through the through hole, whereby an alumina paste layer to be an insulating layer was formed also on the inner wall surface layer of the through hole, and was dried and cured.

Next, 81 parts by weight of Pt powder (average particle size 0.5 μm), 9 parts by weight of alumina powder (average particle size 0.2 μm), 5 parts by weight of ethyl cellulose (binder), 5 parts by weight of butyl carbitol ( A Pt paste B made of a solvent was used to fill the through holes, and then the Pt paste B was dried at 100 ° C. for 30 minutes.

Next, 95 parts by weight of Pt powder (average particle size 0.5 μm), 5 parts by weight of alumina powder (average particle size 0.2 μm), 6 parts by weight of ethyl cellulose (binder), 19 parts by weight of butyl carbitol ( Using a Pt paste C made of a solvent, a Pt paste layer serving as a heating element and a lead terminal was formed on a sheet material on which an alumina paste layer serving as an insulating layer was formed, and then dried at 100 ° C. for 30 minutes. Furthermore, an alumina paste layer serving as an insulating layer was formed on a sheet on which a Pt paste layer was formed using the above-described alumina paste.

(7) Firing First, a porous material made of alumina was embedded in a portion to be a gas diffusion layer of a sheet to be an inspection layer produced by the above-described method. Thereafter, the sheets were laminated in the order of the oxygen pump layer, the inspection layer, the reference layer, the air duct layer, and the beater layer. In addition, between each sheet | seat, the adhesive sheet which consists of insulating resin for adhesion | attachment was inserted, and each sheet | seat was affixed through this adhesive sheet.
The laminate thus produced was degreased and then fired at 1400 to 1500 ° C. to obtain a sintered body of an oxygen concentration detection sensor. At this time, when the total thickness of the heater and the insulating layer was A and the thickness of the insulating layer was B, A / B = 1.05.

(8) Outline processing The end surface of the obtained sintered body is mechanically polished so that the diffusion layer is exposed to the outside air, and the shape (for example, including length adjustment) is adjusted, and the width is 5 mm and the length is 50 mm. An oxygen concentration detection sensor having a thickness of 2 mm was obtained.

(Examples 2 to 14)
The oxygen concentration detection sensor in the same manner as in Example 1 except that the types of metal and ceramic constituting the heater, parts by weight, the A / B, and the porosity of the insulating layer constituting the heater were set to the values shown in Table 1. Manufactured.

(Comparative Examples 1-6)
The oxygen concentration detection sensor in the same manner as in Example 1 except that the types of metal and ceramic constituting the heater, parts by weight, the A / B, and the porosity of the insulating layer constituting the heater were set to the values shown in Table 1. Manufactured.

(Evaluation 1: Appearance observation)
It was observed with a microscope whether or not cracks occurred in the oxygen concentration detection sensors obtained in Examples 1 to 14 and Comparative Examples 1 to 6. The results are shown in Table 1.

(Evaluation 2: Durability test)
After heating the oxygen concentration detection sensors obtained in Examples 1 to 14 and Comparative Examples 1 to 6 to 600 ° C., the temperature was maintained, and it was observed with a microscope whether or not cracks occurred at regular intervals. . The results are shown in Table 1.

In the oxygen concentration detection sensors according to Examples 1 to 14, there were no cracks in the observation after firing, and no cracks occurred even after 100 hours had passed, but in the oxygen concentration detection sensors according to Comparative Examples 1 to 6, Cracks were already generated after firing, and the cracks expanded greatly in 24 hours.

It is a disassembled perspective view which shows typically an example of the oxygen concentration detection sensor of this invention. It is sectional drawing which shows typically the heater layer in the oxygen concentration detection sensor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Oxygen concentration detection sensor 11 Oxygen pump layer 12, 21, 31, 41, 55 Solid electrolyte board 13 Pump upper surface electrode 14 Insulating layer 16 Ground electrode 17 Reference electrode 18 Pump lower surface electrode 20 Inspection layer 22 Gas introduction opening 23 Gas diffusion layer 30 Reference layer 32 Reference upper surface electrode 34 Reference lower surface electrode 40 Air duct layer 42 Notch 50 Heater layer 51 Heater upper layer 52 Heater lower layer 53 Heater 53a Lead part 53b Heat generation part 54a, 54b Insulating layer

Claims (4)

An inspection layer having a gas introduction opening for introducing a gas to be measured containing oxygen;
An oxygen pump comprising a solid electrolyte plate formed on the test layer and having oxygen ion conductivity, a bottom electrode formed on the bottom surface of the solid electrolyte plate, and a top electrode formed on the top surface of the solid electrolyte plate. A functional oxygen pump layer, and
An oxygen concentration detection sensor comprising a heater layer configured to include at least a heater and an insulating layer in which the heater is embedded,
The insulating layer constituting the heater layer has a porosity of 5% or less,
The heater is composed of 90 parts by weight or more of metal and 10 parts by weight or less of at least one selected from the group consisting of alumina, magnesia and spinel. The oxygen concentration detection sensor according to claim 1, wherein the metal constituting the heater is made of Pt or Pt-Au. The heater is composed of 90 parts by weight or more of platinum and 10 parts by weight or less of alumina,
The oxygen concentration detection sensor according to claim 1, wherein an average particle diameter of the alumina is the same as or smaller than an average particle diameter of the platinum. When the total thickness of the heater and the insulating layer is A, and the thickness of the insulating layer is B,
The oxygen concentration detection sensor according to any one of claims 1 to 3, wherein the heater and the insulating layer satisfy a relationship of the following expression (1).
1.0 <A / B ≦ 1.2 (1)

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