JPH0437939B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a gas sensor in which a thick-film detection element and an element support substrate are firmly adhered, and a method for manufacturing the same. Conventionally, as shown in FIG. 1, a gas sensor having a thick-film type detection element formed on the surface of a substrate has electrode patterns 2a and 2b of a desired shape formed by thick-film printing on the surface of an insulating ceramic substrate 1 that supports the detection element. It has been known to form a detection element 3 by printing a thick film of paste containing a gas-sensitive metal oxide as a main component thereon in the shape of the element, and then baking it. This type of sensor has good response due to its thin element, and the heater, which is essential for many gas sensors, can be formed on the same substrate as the detection element by thick film printing, simplifying the structure. , has many advantages. However, in this type of sensor, as can be seen from the cross-sectional view taken along line I-I' in FIG. When used in harsh environments with low adhesive strength and severe thermal cycles such as automobile exhaust, the sensing element may separate from the substrate due to thermal distortion caused by the difference in thermal expansion coefficient between the substrate material and the element material. There was a risk of peeling. In order to eliminate this fear, it is possible to use large ceramic particles as a raw material for the substrate itself to make the substrate surface rough, but on the other hand, such coarse graining may affect the insulation, mechanical strength, etc. of the substrate itself. This results in deterioration of the required properties. As a result of intensive study, the inventors determined that particles were adhered to the element forming surface of the substrate in advance to create irregularities.
It has been found that by forming a thick film detection element thereon, the adhesive strength between the detection element and the support substrate is increased and the possibility of peeling is extremely reduced. The present invention has been made based on the above findings, and its gist is that a support substrate made of insulating sintered ceramics and having a thick film electrode formed on its surface is integrated in the vicinity of the support substrate and the thick film electrode. A group of sintered ceramic particles in which the fixed granulated particles before sintering have an average particle diameter of 5 μm or more and a maximum of 500 μm or less, and are formed on the support substrate and electrically connected to the thick film electrode, and The present invention resides in a gas sensor characterized by comprising a thick film detection element adhered to a particle group. Further, the gist of the present invention, which is related to the above-mentioned specific invention, is to form an electrode pattern of a desired shape on the surface of a green sheet made of insulating ceramic powder and an organic binder by thick film printing, and to form an electrode pattern on the surface of the green sheet. Average particle size 5μm near the above electrode pattern
The method is characterized in that granulated ceramic particles having a maximum particle size of 500 μm or less are dispersed and dotted, then fired, and then a thick film of a paste mainly consisting of a gas-sensitive metal oxide is printed thereon and baked. The problem lies in the manufacturing method of gas sensors. The present invention will be described in detail below with reference to the drawings. First, FIG. 3 is a sectional view showing the state of adhesion between the detection element and the support substrate in the gas sensor of the present invention. Support substrate 1 made of insulating sintered ceramics
Thick film type electrodes 12a, 12b are formed on the surface of the substrate 1, ceramic particle groups 4, 4...4 are integrally fixed to the substrate 11 near the electrodes 12a, 12b, and a detection element 13 is further formed on the surface of the substrate 11. Electrode 12a, 1
2b, and particle groups 4, 4...4
Printed in thick film to adhere to. The first reason why the adhesive strength between the detection element and the supporting substrate of the gas sensor of the present invention is high is that the above-mentioned particle groups 4, 4...4 are present on the substrate surface.
The second reason is that each spherical particle constituting the particle groups 4, 4...4 has a depression 13a, 13a... on the detection element side. ...13a and is thought to function as a hook mutually. Here, the particle group refers to a group of particles starting from unsintered secondary particles granulated into granules, and the particle size range limited above corresponds to the average particle size of these unsintered secondary particles. diameter range. Therefore, the unevenness created by this is much larger than the unevenness caused by normal substrate surface roughness. The average particle size of particle groups 4, 4...4 must be 5 μm or more and the maximum particle size is 500 μm or less before sintering, and if the average particle size is less than 5 μm, the unevenness effect that increases adhesive strength will be poor. , if the thickness exceeds 500 μm, it will be difficult to uniformly form the detection element later by thick film printing, and variations will also increase. The most desirable range of average particle size is 50-200 μm. The amount of particle groups is determined by the visibility depending on the exposed area of the substrate and the particle group when the surface of the substrate before and after sintering on which the particle groups are provided before printing the detection element is viewed from above in a direction perpendicular to the surface. The ratio (hereinafter abbreviated as "coverage ratio") to the blocked area (projected area of the cluster) is 4/1 ~
An amount within the range of 1/4 is desirable, and an optimal amount is an amount where the above ratio is approximately 1/1. The material of the particle group is preferably the same as that of the support substrate 11 because it is easiest to manufacture, but it is also possible to use insulating ceramics of a different material as long as the effects of the present invention are achieved. In terms of mechanical strength, heat resistance, insulation, cost, etc., the most suitable insulating ceramic to be used in the present invention is alumina, followed by mullite, zirconia, and spinel. Next, a method of manufacturing the gas sensor of the present invention will be explained. An insulating ceramic powder and an organic binder are mixed in an organic solvent to form a slurry, and the slurry is formed into a sheet to become the supporting substrate 11 using a doctor blade. Pt, Pd, Rh,
An electrode pattern in a desired shape such as a comb shape or a spiral shape is thick-film printed using a metal paste such as Au or an alloy thereof. Separately, secondary particles made of ceramic powder to form particle groups 4, 4...4 are granulated, and after being dispersed and dotted near the electrode pattern on the surface of the sheet, they are fired, and then mainly
The gas sensor of the present invention is obtained by printing a thick film of a paste made of a gas-sensitive metal oxide such as TiO ₂ or SnO ₂ and optionally containing noble metal powder, and baking the paste. The paste made of gas-sensitive metal oxide becomes the detection element 13 after baking. In the gas sensor of the present invention, as described above, the detection element is bonded onto the substrate in which the depressions are formed due to the large irregularities formed by the particles, and therefore the adhesive strength of the detection element is extremely high. In addition, in the manufacturing method, the above-mentioned irregularities are formed by molding or granulating the substrate and the particle groups separately according to conventional methods, and then sintering them into one piece, so it is a simple process without requiring any special equipment. It has the advantage of being manufactured. As shown in FIG. 4, the gas sensor of the present invention may have a structure in which a protective substrate 6 having an opening 5 is laminated on a supporting substrate 11, and the detection element 13 is printed with a thick film so as to fill the opening 5. . In this case, since the dispersion area of the granulated ceramic particles to form the particle groups 4, 4...4 is limited by the bottom area of the opening 5, uniform dispersion to a predetermined portion is facilitated, and the adhesive strength of the detection element 13 is can be further enhanced. Examples will be described below. Example 12 parts by weight of butyral resin and 6 parts by weight of DBP were added to 100 parts by weight of a mixed powder consisting of 92% by weight of Al ₂ O ₃ , 4% by weight of SiO _{2 ,} 2% by weight of CaO, and 2% by weight of MgO with an average particle size of 1.5 μm. The mixture was mixed in an organic solvent to form a slurry, and a green sheet 21 with a thickness of 1 mm and a green sheet 7 with a thickness of 0.2 mm were produced in the shapes shown in FIGS. 5 and 6 using a doctor blade.
On the surface of the green sheet 21, a heating resistor pattern 8 and an electrode pattern 22a having the shape shown in FIG.
22b is thickly printed with platinum paste, and platinum lead wires 9a, 9b, 9 with a diameter of 0.3 mm are attached to the ends of each pattern.
c was placed. On the other hand, after punching out openings 5 at positions where the tips of the electrode patterns 22a and 22b can be exposed when the green sheet 7 is stacked on the green sheet 21, these two green sheets are laminated and heated. It was crimped. Separately, add 40% to the same powder with the same composition as the mixed powder used for the above sheet.
Parts by weight of polyvinyl alcohol were added, wet-mixed, and granulated into spheres using a spray dryer, followed by sieving into the particle size range shown in Table 1 to obtain granules to be Ceramic Particle Groups 4, 4...4. These granules are scattered on the surface inside the opening 5 so that the coverage ratio is about 1, and the granules are placed in the atmosphere with the two sheets that are crimped together.
It was fired under the conditions of 1500°C and a holding time of 2 hours. Next, 1 mole part of platinum black was added to TiO ₂ powder with an average particle size of 1.2 μm, and 3 parts by weight of ethyl cellulose was added to the total powder, mixed in butyl carbitol, and the viscosity was adjusted to 300 poise. The opening 5 is filled with TiO ₂ paste, and the electrode pattern 22a,
By printing a thick film so as to adhere to the tip of the gas sensor 22b to form the detection element 13, and baking it in the atmosphere at a temperature of 1200°C and a holding time of 1 hour, the gas sensors No. 1 to No. 1 shown in FIG. 8 was manufactured. However, gas sensor No. 1 has aperture 5 for comparison.
The detection element 13 is formed without dispersing the ceramic particles. The internal resistance of gas sensors No. 1 to No. 8 was measured at 350℃ using a propane burner.
The stoichiometric air-fuel ratio λ>
1, all values were 200 MΩ or more, but when λ = 0.9, the values changed to those shown in Table 1, indicating that the sensor function was maintained. A thermal shock test was repeatedly conducted in which the gas sensor was exposed to exhaust gas with a maximum temperature of 800°C from a 2000cc engine under full load for 5 minutes, and then idling for 5 minutes, until the detection element 13 peeled off. Table 1 shows the results of time measurements.

[Table] As can be seen from Table 1, the present invention gas sensor No. 3
- No. 6 had extremely high adhesive strength compared to gas sensors No. 1 to No. 2 of comparative examples. Comparative example gas sensors No. 7 to No. 8 showed adhesive strength comparable to that of the inventive example, but the printing state of the detection element was non-uniform. In order to withstand exposure to intense thermal cycles and vibrations such as automobile exhaust, the substrate is provided with concavities and convexities that have a hook function by concavities formed by granulated particles that are integrated and fixed on the substrate. This is due to the fact that a thick-film thin detection element is formed on top. Moreover, the spherical granulated particles are sprinkled onto a predetermined position on the substrate using the unevenness that has a hook function, without applying compressive force that would cause damage to the substrate.
This was achieved by firing it.

[Brief explanation of drawings]

Figure 1 is a perspective view of a conventional gas sensor; Figure 2 is a perspective view of a conventional gas sensor;
The figures are an enlarged sectional view taken along the line I-I' in FIG. 1, FIG. 3 is a sectional view showing one embodiment of the gas sensor of the present invention, FIG. The figure is a plan view showing the initial stage of the gas sensor manufacturing method of the present invention, FIG. 6 is a plan view showing the middle stage,
FIG. 7 is a plan view showing the same embodiment as FIG. 4. 11... Support substrate, 12a, 12b... Electrode,
4... Ceramic particle group, 13... Detection element, 2
1... Green sheet, 22a, 22b... Electrode pattern.

Claims (1)

[Scope of Claims] 1. A support substrate made of insulating sintered ceramics and having a thick film electrode formed on its surface, a pre-sintered structure that is integrally fixed to the support substrate in the vicinity of the thick film electrode. Particle size is average particle size 5μm or more maximum particle size
The device comprises a group of sintered ceramic particles having a size of 500 μm or less and a thick film detection element formed on the support substrate, electrically connected to the thick film electrode, and adhered to the particle group. Characteristic gas sensor. 2. An electrode pattern of a desired shape is formed on the surface of a green sheet made of insulating ceramic powder and an organic binder by thick film printing, and the average particle size is 5 μm or more and the maximum particle size is 500 μm on the surface of the green sheet near the electrode pattern. A method for producing a gas sensor, which comprises dispersing the following group of granulated ceramic particles, then firing, and then printing a thick film of paste mainly consisting of a gas-sensitive metal oxide thereon and baking it.