JP2003130842A - Oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen sensor that can solve the problem that a diffusion control layer or protection layer formed by flame spray coating is remarkably low in holding strength, and the diffusion control layer or protection layer on the surface of a zirconia solid-state electrolyte is easily peeled off by vibration of a real car. SOLUTION: A roughened surface of 1.0 μm in surface roughness (Ra) is formed around a measuring electrode, and a diffusion control layer is formed to cover the roughened surface portion and the measuring electrode.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxygen sensor for detecting a ratio of air to fuel in an internal combustion engine of an automobile or the like.

[0002]

2. Description of the Related Art Currently, in internal combustion engines such as automobiles,
By detecting the oxygen concentration in the exhaust gas and controlling the supply amount of air and fuel supplied to the internal combustion engine based on the detected value, harmful substances such as CO and H from the internal combustion engine can be controlled.
A method of reducing C and NOx is adopted.

As an oxygen sensor element for detecting such oxygen concentration, as shown in FIG. 4, an air chamber 28 is provided inside a zirconia solid electrolyte having oxygen ion conductivity, and Pt is provided on the outer surface of the zirconia solid electrolyte. And a reference electrode 25 made of Pt on the surface of the zirconia solid electrolyte on the air chamber side facing the measurement electrode 24.
From the solid electrolyte layer 23 having the above, the zirconia solid electrolyte 23 in the portion facing the sensor cell with the air chamber 28 and the air introduction hole 29 interposed therebetween, and the solid electrolyte layer 30 serving as the side wall of the air chamber 28 and the air introduction hole 29. Heating element 3 sandwiched between the sensor substrate 21 and the ceramic insulator 31.
2 and the heater substrate 22 in which the electrode lead-out portion 34 is embedded is proposed (Japanese Patent Laid-Open No. 10-1327).
No. 80). In the exhaust gas, a diffusion rate controlling layer 37 is formed on the measurement electrode 24, and a voltage of about 0.4 to 0.8 V is applied so that the reference electrode 25 side is + and the measurement electrode 24 side is −. It was designed to detect the limiting current commensurate with the oxygen concentration of.

This oxygen sensor operates so as to pump oxygen from the exhaust gas into the air chamber 28 if the exhaust gas is in an air-rich atmosphere, and in the exhaust gas if the exhaust gas is fuel-rich. The electromotive force generated by the oxygen concentration ratio between the air chamber 28 and the air chamber 28 operates to pump oxygen from the air chamber 28 into the exhaust gas.

[0005]

However, the diffusion-controlling layer formed on the measuring electrode is usually formed by thermal spraying, but the surface of the solid electrolyte made of zirconia is very smooth and is formed by thermal spraying. It was found that the diffusion-controlling layer or the protective layer had a very low holding strength, and the diffusion-controlling layer or the protective layer on the surface of the zirconia solid electrolyte was easily peeled off by the vibration of the actual vehicle.

Further, there is a problem in that the air-fuel ratio cannot be accurately detected due to the partial separation of the diffusion-controlling layer.

[0007]

Means for Solving the Problems According to the present invention, a measurement electrode is provided on the outer surface of a solid electrolyte substrate having an air introduction hole whose one end is sealed, and a reference electrode is provided on the air introduction hole-side inner surface facing the measurement electrode. And a diffusion rate controlling layer so as to cover the rough surface portion and the measuring electrode, while forming a rough surface portion having a surface roughness (Ra) of 1.0 μm or more around the measuring electrode. And The surface roughness in the present invention is the arithmetic average roughness (Ra).

Further, the rough surface portion is composed of a coating layer formed on the solid electrolyte substrate.

The thickness of the coating layer is 5 to 200 μm.
m, and the width is 0.5 to 2.0 mm.

Further, the coating layer is characterized by containing alumina as a main component.

Further, the coating layer is formed within 1.5 mm from the outer edge of the measuring electrode.

Further, the coating layer is characterized in that it surrounds the measuring electrode in a broken line shape.

By forming such a coating layer,
By increasing the adhesion strength of the diffusion-controlling layer and the protective layer of the measuring electrode to the measuring electrode, it becomes possible to form the diffusion-controlling layer and the protective layer having good durability.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the oxygen sensor element of the present invention is shown in FIGS.

This oxygen sensor element 1 comprises a fixed electrolyte layer 3 made of zirconia and a measurement electrode 4, a reference electrode 5 and an electrode lead-out portion 6 electrode pad 7 formed on the opposing surface.
And an air chamber 8 formed so as to cover the reference electrode 5 and an air introduction hole 9 connected to it and having one end opened
A sensor element 1 comprising a solid electrolyte layer 10 serving as a side wall of these, a solid electrolyte layer 3 positioned to face the solid electrolyte layer 3 and serving as a lid for the air chamber 8 and the air introduction hole 9, and ceramic insulation It is composed of a heater element 10 in which a heating element 12 is built in a body 11. The sensor element 1 and the heater element 2 are assembled and fixed so that the heat generating portion of the heater element 2 is in contact with each other.

A coating layer 16 is formed as a rough surface portion around the measuring electrode 4, and the coating layer 16 and the measuring electrode 4 are provided.
A diffusion-controlling layer 17 made of porous zirconia, a spinel sprayed film, alumina or the like is formed on the surface of the. The diffusion-controlling layer 17 serves both as a protection layer against poisoning from exhaust gas and as the diffusion-controlling layer 17 of the limiting current element.

In order to firmly fix the diffusion-controlling layer 17 around the measuring electrode 4 of the sensor substrate 1, the surface roughness (Ra) of the rough surface portion of the sensor substrate 1 is preferably 1.0 μm or more. . If the surface roughness (Ra) is 1.0 μm or less, the anchor effect becomes weak, which is not preferable. The surface roughness (Ra) of the surface of the sintered solid electrolyte layer 3 is 0.2 μm.
It is very smooth as below. The surface roughness (Ra) of the measurement electrode 4 and the reference electrode 5 is 2.0 to 7.0 μm.
Since it is m, it is considered that the diffusion-controlling layer 17 due to thermal spraying is easily fixed. The surface roughness (Ra) is more preferably 2.0 μm or more.

In order to set the surface roughness (Ra) of the rough surface portion formed around the measurement electrode 4 to 1 μm or more, a coating layer 16 may be formed around the measurement electrode 4 as shown in FIG.
The coating layer 16 functions as an anchor for fixing the diffusion control layer 17 to the sensor substrate 1. Measuring electrode 4
However, since the surface of the solid electrolyte layer 3 is very smooth, the adhesion of the diffusion-controlling layer 17 is low. Without the coating layer 16, the solid electrolyte layer 3 peels off due to the heat cycle during use, and also partially peels off from the surface of the measurement electrode 4, which makes it impossible to accurately detect the air-fuel ratio.

The coating layer 16 has a thickness of 5 to 200 μm.
It is preferably m. When the thickness is 5 μm or less, the surface roughness Rmax becomes small and a sufficient anchor effect cannot be expected. If the thickness exceeds 200 μm, the warpage of the sensor substrate 1 is affected, which is not preferable. When the warp of the sensor substrate 1 exceeds 100 μm, the contact with the heater substrate 2 becomes poor, and the temperature rise during heating is slowed, and the sensor substrate 1 and the heater substrate 2 come into partial contact, causing wear and cracks. It is not preferable because it causes the generation.

The coating layer 16 is preferably formed within 1.5 mm from the outer edge of the measuring electrode 4. When it is formed over 1.5 mm away from the outer periphery of the measuring electrode 4,
This is because the portion between the coating layer 16 and the measurement electrode 4 may peel off.

The coating layer 16 is preferably formed by applying a paste containing alumina ceramics as a main component on the surface of the solid electrolyte layer 3 and simultaneously firing it. At this time, as the sintering proceeds, the sintering aid added to the alumina ceramics diffuses into the solid electrolyte layer 3, and the coating layer 16 becomes porous in alumina. By such a reaction, the coating layer 16 can be firmly fixed to the surface of the solid electrolyte layer 3. Further, it was found that utilizing this porous structure as an anchor for the diffusion-controlling layer 17 is effective for improving the fixing strength of the diffusion-controlling layer 17 and improving the durability.

As another method for producing the coating layer 16, a paste obtained by adding a resin-made pore material to a raw material having the same composition as the solid electrolyte layer 3 is printed on the surface of the solid electrolyte layer 3 to form the solid electrolyte layer 3 with the solid electrolyte layer 3. The porous coating layer 16 may be formed by simultaneous firing. In this case, the coating layer 1 has the same composition.
6 can be firmly fixed to the surface of the solid electrolyte layer 3. Moreover, the surface roughness (Ra) of the solid electrolyte layer 3 around the measuring electrode 4 is 1 μm by covering the measuring electrode 4 with a mask and protecting the measuring electrode 4 by blasting.
It may be m or more.

Further, as shown in FIG. 3, the coating layer 16 may be installed so as to surround the measuring electrode 4 in a broken line shape. As a merit of such a configuration, there is an effect of reducing occurrence of warpage due to firing shrinkage of the solid electrolyte layer 3 and the coating layer 16 or a difference in coefficient of thermal expansion. Further, regarding the shape of the broken line, it is preferable that the length of the solid line portion is 1 mm or more and the pitch thereof is 1 mm or less.

The reference electrode 4 and the measurement electrode 4 are Pt.
20 to 70% by volume of zirconia powder was added to the powder and sintered, and each was composed of a porous platinum electrode and formed a large number of solid electrolyte-Pt-gas phase triple points, and gas. Has a structure that allows easy diffusion. Further, the added zirconia powder is sintered with the solid electrolyte layer 3 to firmly fix the electrode to the solid electrolyte layer 3.

On the other hand, the heater substrate 2 includes a heating resistor 12 made of a high melting point metal such as W, Mo and Re, and a lead electrode 14.
It has a structure in which the
Like the sensor substrate 1, it has a flat plate shape.
The heating resistor 12 is connected to the electrode pad 13 formed on the surface of the insulating layer 11 and has a structure that heats when the electrode pad 13 is energized. The composition of the heating element 12 may be appropriately selected depending on the heating capacity and the temperature rising rate. In this case, it is preferable that the resistance ratio between the heating resistor 12 and the lead portion 14 be controlled within the range of 9: 1 to 7: 3 at room temperature.

Next, the operation of the sensor substrate 1 will be described. When the air-fuel ratio is excessively air, a positive current due to the voltage applied to the measurement electrode 4 and the reference electrode 5 flows, but when the air-fuel ratio is on the fuel excess side, an air chamber 7 is formed between the measurement electrode 4 and the reference electrode 5. Electromotive force is generated according to the oxygen concentration ratio of the exhaust gas,
Since the electromotive force becomes larger than the voltage, a current that pumps the air on the air chamber 7 side into the exhaust gas flows.

This oxygen sensor has a voltage of 0.4 so that the measuring electrode 4 becomes negative and the reference electrode 5 becomes positive.
A voltage of ˜0.8 V is applied to pump oxygen in the exhaust gas to the air chamber 8 side. At this time, a current proportional to the air-fuel ratio flows due to the presence of the diffusion control layer 17, and the air-fuel ratio can be detected by measuring this current value. Conventionally, the development has been advanced with the aim of increasing the heating efficiency of the sensor substrate 1 by incorporating the heater part in the sensor substrate 1, but now, it is shifting to the direction of cost priority and high melting point. Heating resistor 1 made of metal
The mainstream direction is to separately combine the heater elements 2 having the built-in elements 2.

As another embodiment of the present invention, the heater part may be integrated with the sensor substrate 1. When using a heater integrated oxygen sensor with a built-in heater,
The heating element 12 is made of Pt as a main component.

On the other hand, the heater substrate 2 of the oxygen sensor 1 of the type in which the sensor substrate 1 and the heater substrate 2 are used in combination,
The heating resistor 12 made of W, Mo, Re or the like is embedded in the insulating layer 11 having the same flat plate shape as that of the sensor substrate 1 and containing alumina as a main component. In the present invention, in order to efficiently overheat the sensor substrate 1, the distance from the heating resistor 12 to the surface of the heater substrate 2 in contact with the sensor substrate 1 is preferably 200 to 600 μm. If the distance is less than 200 μm, the heat resistance of the heater substrate 2 deteriorates. Further, if the distance exceeds 600 μm, the heat transfer from the heater substrate 2 to the sensor substrate 1 deteriorates, and as a result, the gas responsiveness of the sensor substrate 1 deteriorates. The distance from the heating resistor 12 to the surface of the heater substrate 2 in contact with the sensor substrate 1 is particularly 300 to 400 μm.
Is desirable.

Further, the thickness of the heater substrate 2 is 0.7 to
2 mm, particularly 1 to 1.5 mm is preferable from the viewpoint of strength. When the thickness of the heater substrate 2 is less than 0.7 mm, the strength of the heater substrate 2 is low, and when it exceeds 2 mm, the heater substrate 2 is too thin.
Also, a large amount of electricity is required to heat the sensor substrate 1 adjacent thereto, which is not preferable.

Further, the heating resistor 12 embedded in the heater substrate 2 has W, Mo, R due to the relationship between heat resistance and manufacturing cost.
It is desirable to be composed of one or more of e. As the structure of the heating resistor 12, it is possible to use either a structure folded back to the left or the right or a structure folded back in the longitudinal direction.

Next, the constituent elements of the sensor substrate 2 will be described.

The surface of the measuring electrode 4 which is in direct contact with the exhaust gas has a function of protecting the electrode from poisonous substances in the exhaust gas, and the other is the purpose of controlling the diffusion amount of oxygen from the exhaust gas to the measuring electrode 4. With a thickness of 10 to 800 μm and a porosity of 10 to 5
A diffusion rate controlling layer 17 made of a ceramic porous layer made of 0% zirconia, alumina, γ-alumina, spinel and the like is provided. The thickness of the diffusion control layer 17 is 1
If the thickness is less than 0 μm or the porosity exceeds 50%, the electrode poisoning substances P, Si, etc. easily reach the electrode and the electrode performance deteriorates. On the other hand, if the thickness of the diffusion-controlling layer 17 exceeds 800 μm or the porosity becomes less than 10%, the diffusion rate of gas in the porous layer becomes slow,
The gas response of the electrode deteriorates. In particular, depending on the pore diameter, the thickness of the diffusion-controlling layer 17 is 100 to 500 μm.
Is excellent. Further, the diffusion-controlling layer 17 may be formed by controlling the pore diameter and the thickness of the diffusion-controlling layer 15 so that the limiting current value in the atmosphere is about 3 to 10 mA.

The measuring electrode 4 and the reference electrode 5, which are adhered and formed on the surface of the solid electrolyte layer 3, the electrode lead-out portion 6, and the electrode pad 7.
In each case, platinum or an alloy of platinum and one kind selected from the group of rhodium, palladium, ruthenium and gold is used. Further, for the purpose of preventing grain growth of metal in the electrode during sensor operation, and for increasing the so-called three-phase interface contact point between the metal particles, solid electrolyte and gas contained in the electrode relating to responsiveness, The above-mentioned ceramic solid electrolyte component may be mixed in the electrode in a proportion of 1 to 50% by volume, particularly 10 to 30% by volume. Regarding the electrode lead-out portion 6 and the electrode pad 9, the solid electrolyte component to be added plays a role of increasing the adhesion strength with the solid electrolyte layer 3 as the base material.

The shape of the electrodes may be square or elliptical. Further, the thickness of the electrode is preferably 3 to 20 μm, and particularly preferably 5 to 10 μm.

Next, a method of manufacturing the heater substrate 2 will be described.

The alumina green sheet is prepared by adding a molding organic binder to alumina powder as appropriate by a known method such as a doctor blade method, extrusion molding, hydrostatic molding (rubber press) or press forming. At this time, as the alumina powder, a powder containing alumina as a main component and containing Mg, Ca, and Si in a total amount of 1 to 10 wt% is preferably used for the purpose of improving sinterability. In addition, alkali metals such as Na and K migrate and are concentrated on the cathode side, lower the melting point of the surrounding ceramic insulator 12, promote the concentration of other alkaline earth metals, and oxidize these metal elements. 0.1 wt% because cracks are generated in the ceramic insulator 11 on the cathode side due to the movement of the object and the electrical insulation and the durability of the heating element 12 are deteriorated.
The following needs to be controlled.

On one side of the above green sheet, W, Mo,
After forming a pattern of the heating resistor 12 by a slurry dip method, screen printing, pad printing, or roll transfer using a conductive paste containing Re or the like, a green sheet is formed by interposing an adhesive such as an acrylic resin or an organic solvent. Are bonded or mechanically bonded while applying pressure with a roller or the like to produce a laminated body of the heater substrates 2.

The heating of the heater substrate 2 is performed for 5 to 10 hours in a temperature range of 1400 ° C. to 1650 ° C. in a reducing gas atmosphere such as forming containing hydrogen and the like from the viewpoint of preventing the heating resistor 12 from being oxidized. At this time, in order to suppress the warp of the heater substrate 2 during firing, the amount of warp can be reduced by placing a smooth substrate such as alumina as a weight on the laminated body so as to apply a weight.

Next, an example of a method for manufacturing the sensor substrate 1 of the present invention will be described. Sensor substrate 1 of oxygen sensor 1 of the present invention
As shown in FIG. 1, the measurement electrode 4 and the reference electrode 5 are formed on the both surfaces of the solid electrolyte layer 3 made of the zirconia green sheet by using a conductive paste containing platinum, or by a slurry dip method, screen printing, or pad printing. Then, a ceramic porous layer that becomes the diffusion-controlling layer 17 is formed on the surface of the measurement electrode 4, and then air is formed on the surface of the solid electrolyte layer 3 made of the zirconia green sheet on the reference electrode 5 side. After forming the solid electrolyte layer 10 which becomes the side wall of the chamber 8 and the air introduction hole 9, another solid electrolyte layer 3 is further laminated. At this time, the lamination can be performed by interposing an adhesive such as an acrylic resin or an organic solvent between the green sheets for adhesion, or by mechanically adhering while applying pressure with a roller or the like. Firing is performed in the air or in an inert gas atmosphere at 13
It is carried out in the temperature range of 00 ° C to 1500 ° C for 1 to 10 hours.

After that, the heater substrate 2 produced separately,
The sensor substrate 1 is fixed and an oxygen sensor is manufactured.

[0042]

EXAMPLE 1 An example of the present invention will be described by taking the air-fuel ratio sensor element shown in FIG. 1 as an example.

It consists of commercially available alumina powder containing 5 wt% of oxides of Si, Mg and Ca, zirconia powder containing 5 wt% Y ₂ O ₃ containing 0.1 wt% of Si, and 8 mol% yttria. Platinum powder containing 30% by volume of zirconia powder and W powder were prepared.

First, a polyvinyl alcohol solution was added to zirconia powder containing 5 mol% Y ₂ O ₃ to prepare a kneaded material, and a green sheet of zirconia was formed by extrusion molding so as to have a thickness of 0.4 mm after sintering. It was made. After that, platinum containing zirconia powder was screen-printed on both sides of the green sheet to prepare the measurement electrode 4 and the reference electrode 5, and then the coating layer 16 to be the rough surface portion was formed 0.5 mm from the outer circumference of the measurement electrode 4. The zirconia green sheet forming the side wall of the air chamber 7 and the air introduction hole 8 is adhered to the main surface of the reference electrode 5 side by using an adhesion liquid containing an acrylic binder, The air chamber 7 and the green sheet that will be the lid of the air introduction hole 8 were brought into close contact with each other to form a laminate, which was then baked at 1450 ° C. for 2 hours to obtain the sensor substrate 1.

At this time, the alumina used for the coating layer 16 had a mean particle size varied from 0.2 to 2.0 μm. Further, the surface roughness (Ra) of the coating layer 16 was adjusted by adjusting the concentration and viscosity of the paste prepared for the coating layer 16. In addition, in the paste for the coating layer 16 made of alumina or zirconia, 3 parts of a pore material having an average particle diameter of 30 μm is used.
A sample in which 0 volume% was added to adjust the surface roughness (Ra) of these pastes after sintering was also prepared. In addition,
The surface roughness (Ra) of the coating layer 16 was measured with a surface roughness meter before forming the diffusion controlling layer 17.

Then, a diffusion controlling layer 17 made of spinel was formed on the measuring electrode 4 and the coating layer 16 to a thickness of 400 μm.

On the other hand, a polyvinyl alcohol solution was added to alumina powder to prepare a kneaded clay, which had a thickness of 0.1 to 10 after firing.
Green sheets of various aluminas were produced by extrusion so as to have a thickness of 0.8 mm. After that, the heating element 12 made of W is printed on the green sheet by screen printing so as to have a thickness of about 40 μm, and further, alumina green sheets are stacked using an acrylic adhesive to form a laminate, and then 1500 Sintered in nitrogen gas containing 10% of hydrogen at 10 ° C. for 10 hours to have the same width as the sensor substrate 1 and a thickness of 1.
A 5 mm heater substrate 2 was produced.

After that, the sensor substrate 1 and the heater substrate 2 are linked and fixed, and the heater substrate 2 is heated so that the surface of the diffusion control layer 17 of the sensor substrate 1 is heated to 1000 ° C. in 1 minute. Diffusion rate controlling layer 17 after repeating a cycle of cooling to 40 ° C. or less for 2 minutes for 5000 cycles
The presence or absence of peeling was confirmed for each of the 10 conditions.

Regarding the presence or absence of peeling, a peeling test in which a commercially available gum tape was attached to the surface of the diffusion-controlling layer 17 and then peeling was repeated for 3 cycles, and the presence or absence of peeling was confirmed using a 20 times double application.

The results are shown in Table 1.

[0051]

[Table 1]

As can be seen from Table 1, No. 1 whose surface roughness (Ra) of the coating layer 16 is less than 1.0 μm. In No. 1 and No. 2 in the peeling test after the temperature rising test, peeling of the diffusion-controlling layer 17 occurred in more than half of them. On the other hand, the coating layer 16
Whose surface roughness (Ra) is 1.0 μm or more. 3-
Sample No. 7 showed good performance with almost no peeling. No.
In No. 3, although peeling was observed in a part of the diffusion-controlling layer 17 on the coating layer 16, the diffusion-controlling performance was not affected.

Example 2 Here, the diffusion-controlling layer 1 with respect to the thickness and width of the coating layer 16 was used.
The change in fixing strength of No. 7 was investigated.

A sample was prepared in the same manner as in Example 1,
A sample in which the thickness of the coating layer 16 made of alumina was varied between 2 and 250 μm and the width was varied between 0.2 and 2.5 mm was prepared.

After that, the sensor substrate 2 and the heater substrate 10 are connected and fixed to each other, and a free end length of 20 mm is set in the vibration tester.
Set 10 conditions each and set the amplitude to 1.0
100 cycles of a test of fixing to mm and increasing from 0 to 30 G in 20 minutes and lowering in 20 minutes are carried out, and a peeling test of sticking a commercially available gum tape on the surface of the diffusion-controlling layer 17 and then peeling is repeated 3 times to obtain 20 times. The presence or absence of peeling was confirmed using the above-mentioned Sogan.

The warpage of the sensor substrate 1 was measured using a surface roughness meter. The amount of warpage per inch of length was measured around the measuring electrode 4. Regarding the measurement electrode 4 portion, the thickness of the electrode was measured by the step difference at the end portion, and the amount of warpage was corrected. The criterion for the amount of warp was NG if it exceeded 200 μm, and OK if it was 200 μm or less.

The results are shown in Table 2.

[0058]

[Table 2]

As can be seen from the results in Table 2, the coating layer 16 having a thickness of less than 5 μm has a thickness of less than 5 μm. In No. 1, peeling of the diffusion-controlling layer 17 occurred in some samples. Moreover, the width of the coating layer 16 is less than 0.5 mm. In 9 as well, peeling occurred in some samples. In addition, the thickness of the coating layer 16 is 200μ
No. over m. No. 8 and a width of 2 mm or more.
In No. 14, warp of 100 μm or more occurred in the sensor substrate 1, and in part of the sensor substrate 1, the coating layer 16 had a thickness of 5 to 200 μm. 2-7, 10-13,
In No. 15, peeling of the diffusion control layer 17 did not occur.

[0060]

As described above in detail, according to the present invention, the measuring electrode is provided on the outer surface of the solid electrolyte substrate having the air introducing hole whose one end is sealed, and the side of the atmosphere introducing hole facing the measuring electrode is provided. A reference electrode is provided on each inner surface, and a rough surface portion having a surface roughness (Ra) of 1.0 μm or more is formed around the measurement electrode, and a diffusion rate controlling layer is formed so as to cover the rough surface portion and the measurement electrode. By doing so, the fixing strength of the diffusion-controlling layer or the protective layer formed on the surface of the measurement electrode can be increased, and an oxygen sensor with good durability can be provided.

[Brief description of drawings]

FIG. 1 is a developed perspective view showing an example of an oxygen sensor of the present invention.

FIG. 2 is a plan view showing another embodiment of the oxygen sensor of the present invention.

FIG. 3 is a plan view showing another embodiment of the oxygen sensor of the present invention.

FIG. 4 is a developed perspective view showing another example of a conventional oxygen sensor.

[Explanation of symbols]

1 sensor board 2 heater substrate 3 Solid electrolyte layer 4 measuring electrodes 5 Reference electrode 6 lead electrode 7 electrode pad 8 air chambers 9 Air introduction hole 10 Air chamber side wall 11 insulating layer 12 Heating resistor 13 electrode pads 14 Lead electrode 15 beer hall 16 coating layer 17 Diffusion rate controlling layer

Claims (5)

[Claims] 1. A measurement electrode is provided on the outer surface of a solid electrolyte substrate having an air introduction hole whose one end is sealed, and a reference electrode is provided on the atmosphere introduction hole side inner surface facing the measurement electrode. An oxygen sensor, characterized in that a rough surface portion having a surface roughness (Ra) of 1.0 μm or more is formed around, and a diffusion-controlling layer is provided so as to cover the rough surface portion and the measurement electrode. 2. The oxygen sensor according to claim 1, wherein the rough surface portion comprises a coating layer formed on a solid electrolyte substrate. 3. The oxygen sensor according to claim 2, wherein the coating layer has a thickness of 5 to 200 μm and a width of 0.5 to 2.0 mm. 4. The oxygen sensor according to claim 2, wherein the coating layer contains alumina as a main component. 5. The oxygen sensor according to claim 2, wherein the coating layer surrounds the measuring electrode in a broken line shape.