JPH051900B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of industrial application) Thick film devices are increasingly being applied in line with recent advances in hybrid technology. For example, when making a sensor by depositing a metal oxide semiconductor thick film, or making a ceramic capacitor by depositing a highly dielectric metal oxide thick film on a ceramic substrate, or for example, Si ₃ N ₄ Various applications are currently underway, such as forming a protective coating layer such as Al ₂ O ₃ on the surface of aluminum to improve its corrosion resistance and oxidation resistance. The technical content described in this specification regarding the improvement of this type of thick film element is the development result of a fundamental improvement in the adhesion between the thick film and the ceramic insulating substrate, which is a technical problem common to various thick films. This is where we propose. [Prior Art] For some types of thick film devices, additives are used in the thick film material to help improve adhesion, such as glass. et al Int.
Microelectronics Symp. (1971) 4.7) and Proceedings Institute Electroradio Engineering Conference 1976.
(MV Coleman et: Proc.Inst.Electro.Radio
Eng. Conf. (1976) [31] 1-16), etc., but additives often force the thick film element itself to change in quality. Another method is to choose a combination of a substrate and a thick film with a similar coefficient of thermal expansion.
H.Kohl “Materials and Techniques for
Vacum Devices”p391 (1967) Reinhold Pub.)
As shown in , thermal strain is reduced by approximating the coefficient of thermal expansion, and even if the adhesion strength is somewhat low, it is quite effective in preventing peeling. However, it does not have sufficient resistance to mechanical shock. In addition to these, it is often done to increase the adhesion of thick films by roughening the surface of the substrate. Attempts have been made to roughen the surface using a projection method or to coat the surface of the substrate with coarse crystal grains to make use of the unevenness, but the sintering properties of the two differ due to the difference in crystal grain size from the base material, resulting in poor results. It was not possible to obtain proper adhesion or to obtain uniform and controlled unevenness.
Furthermore, it is difficult to obtain sufficient adhesion, especially for thick films of 10 μm or more, and the roughening of the former damages the surface of the substrate, which is disadvantageous in terms of basic strength. Furthermore, these conventional techniques do not apply at least to those related to the fixation of functional semiconductor thick films. (Problems to be Solved by the Invention) When a thick film, particularly a film thickness of 10 μm or more, is required, a metal that can be deposited with high adhesion strength on the surface of a ceramic insulating substrate. It is an object of the invention to provide a ceramic substrate carrying a thick oxide film. (Means for Solving the Problems) The above object can be advantageously achieved by a configuration based on the following points. That is, in this invention, a thick film of metal oxides is baked on the surface of a ceramic insulating base, and the surface of the ceramic insulating base is
A group of fired ceramic particles with an average particle size of 5 μm or more and a maximum particle size of 500 μm or less are dispersed and coalesced in a ceramic insulating substrate by 1/20 to 1/4 of the average particle size while being partially buried in the substrate, and formed on the surface of the substrate. It has an uneven base,
Carrying a thick metal oxide film on the uneven base, which is characterized by forming a baked thick film layer of a metal oxide filling the inside of the uneven base.
It is a ceramic substrate. Here, ceramic insulating substrates can be made of metal oxides such as alumina, beryllia, forsterite, zirconia, chitavari, ferrite, and non-oxides such as silicon nitride and aluminum nitride. . For the fired ceramic particles used to ensure firm adhesion of the metal oxide thick film on the surface of these ceramic insulating substrates, it is advantageous to use materials that are the same or similar to those of the substrate, especially those with similar sintering properties. Of course, it does not matter if it is made of a different material if there is one. Fired ceramic particles are advantageously suitable here as granulated particles in an unfired state with an average particle size of 5 μm or more, preferably 50 to 200 μm, and a maximum particle size of 500 μm, particularly 300 μm or less. If the average particle size is smaller than 5 μm, it is difficult to produce a locking effect that is useful for ensuring adhesion strength, especially for thick films, while particles with a maximum particle size of more than 500 μm, for example, cannot be used for thick films of sensing functional semiconductors. However, it is difficult to form the film uniformly using a conventional thick film printing method, and when it is used as a functional element, the thick film tends to have uneven properties. Partial embedding of fired ceramic particles on the surface of the ceramic insulating substrate is approximately 1/20 of the average particle diameter.
It is preferable to make the depth about 1/4, 1/20
If it is shallower, the fired ceramic particles will likely bite into the particles and will not adhere properly, while if they are buried too deep (more than 1/4 of the way), the work will be difficult and the subsequent deposition of the sensing functional semiconductor thick film will be difficult. In some cases, there is a disadvantage that it is difficult to expect a sufficient hook-like restraint effect. The density of the buried ceramic fired particles is determined by the ratio of the vertically exposed area of the surface of the ceramic insulating substrate itself to the vertically covered area by the dispersed particles (hereinafter referred to as coverage ratio) of 1:4 to 1:4.
The coverage ratio is preferably in the range of 4:1, and the optimum coverage ratio is 1:1, but it can be selected as appropriate depending on the intended use of the membrane. As for the material of the fired ceramic particles, as already mentioned in relation to the material of the ceramic insulating substrate, we selected alumina as the best material, taking into consideration mechanical strength, heat resistance, insulation, and price. Mullite, zirconia, and spinel are also suitable. The method for manufacturing a ceramic substrate according to the present invention will be exemplified as follows. First, for a ceramic insulating substrate, a slurry is prepared by mixing ceramic powder mixed with an organic binder in an organic solvent, and a green sheet to be used as the substrate is formed by, for example, a doctor blade method. Pt, Pd,
A desired electrode pattern is thick-film printed in a predetermined shape, such as a comb shape or a spiral shape, using a metal paste such as Rh, Au, or an alloy thereof. Although it is more preferable to perform this electrode forming step in this order, it is not essential and may be performed after the formation of the uneven base surface described later. Moreover, it goes without saying that this electrode forming step is skipped if the purpose is simply to coat a foreign substance on ceramic. On the other hand, ceramic powder is separately granulated to a particle size within the above-mentioned range using a conventional method, preferably using a spray dryer. The heat-treated and temporarily solidified particles are scattered at key points on the surface of the green sheet, for example near the electrode pattern, so that the coverage ratio as described above is achieved, and each particle is It is only necessary to cause partial embedding during the dispersion of the granulated particles, so that the shape of the granulated particles is maintained here.
It is also desirable to interpose a cushion sheet as a pressurizing flat plate. Furthermore, ceramic fired particles are
In order to integrate the particles into the substrate under partial burying, the method is not limited to pressing the particles, but it is also possible to apply a mixture of granulated particles and bonding fine particles in a suspension liquid in advance onto the raw substrate surface. By keeping the fine particles in place, the fine particles are deposited at the foot of the granulated particles so that the granulated particles are buried at a predetermined depth.
It may be integrated and sintered, or the surface of the green sheet may be coated with a solvent and the granulated particles may simply be dispersed therein. In this way, the ceramic green sheet is
After granulation and dispersion of raw particles in an embedded manner, sintering is carried out under temperature conditions compatible with their sintering, followed by TiO ₂ , SnO, etc., which are useful for depositing, for example, semiconductor thick films with sensing functionality. ₂ , ZnO, and gas-sensitive metal oxide powders such as Fe ₂ O ₃ , with the above-mentioned metal paste components added as necessary.
A ceramic substrate carrying a thick film can be obtained by applying the thick film paste by thick film printing or casting and baking. In this way, for example, a sensing functional semiconductor thick film can be supported on a ceramic insulating substrate on an uneven base formed of ceramic sintered particles, which are buried and almost uniformly distributed and integrated on the substrate. This is due to the baking of the thick film paste that has penetrated between the layers, so the adhesion strength between the thick film itself and the uneven substrate is extremely high.Moreover, in the case of a sensing functional semiconductor thick film, the functional semiconductor thickness has particularly stable performance. A membrane element is obtained. Now, FIG. 1 schematically shows a cross section across the plate surface of a ceramic substrate according to the present invention, in which 1 is a ceramic insulating base, 2 is ceramic fired particles that have coalesced under partial burial on the surface of the base, and 3 is a An uneven base formed on the substrate surface by dispersing the particles, and 4
This is a baked thick film layer of metal oxides formed on the uneven base 3 and filling the spaces between the uneven base 3. 5 indicates the electrode layer in this example. (Function) The ceramic insulating substrate 1 originally has a surface roughness as shown in FIG. However, according to the present invention, for example, the particle size is approximately 30 μm.
As illustrated in Fig. 2c for a case in which ceramic sintered particles 2 having a spherical shape are buried in the surface of the ceramic insulating substrate 1 by several micrometers, the unevenness is characteristic in that the degree of surface roughening is particularly remarkable. Obtain base 3. As is clear from FIGS. 1 and 2c, this uneven base 3 has uneven gaps that widen toward the surface of the ceramic insulating base 1 between the dispersed ceramic fired particles 2. Therefore, the hardening of the baked thick film layer 4 that fills the inside of the gap is firmly achieved. In fact, the above-mentioned hardening effect can be sufficiently achieved by uniformly dispersing the ceramic sintered particles in the area covered with the baked thick film layer 4 on the surface of the ceramic insulating substrate 1. Embodiments of the present invention as a thick film gas sensor will be mainly described below. FIG. 3 shows the external appearance of this type of gas sensor. In the figure, 5a and 5b are electrodes provided on a ceramic insulating substrate 1. Conventionally, a baked thick film layer 4 as a gas detection film is provided between the electrodes 5a and 5b. However, due to insufficient adhesion, the internal resistance of the sensor often changes, especially when used in harsh temperature environments with severe thermal cycles such as automobile exhaust gas. Due to thermal strain caused by the difference in coefficient of thermal expansion between the base body 1 and the baked thick film layer 5, there was a problem in that the function of the sensor was quickly impaired due to peeling of the baked thick film layer 4. Note that such examples are not limited to gas sensors, but also include thermosensors that use a thermistor film as an adhesion layer on a ceramic insulating substrate, humidity sensors that use moisture-sensitive materials, and other resistive elements that use resistor films. This is common to functional devices that use a sensing functional semiconductor thick film, such as thick film capacitors that use a dielectric film, and in addition, the adhesion strength between a ceramic coating layer of a dissimilar material and the ceramic body, which is simply a protective film. It is clear that this invention is useful for all purposes. In this invention, as shown in the cross-sectional view in FIG. by,
Since the roots are hardened through the uneven base 3, the adhesion is strengthened by expanding the adhesion area due to the unevenness and by the hook-like restraint of the baked thick film layer 5 that fills the inside of the gap between the particles and penetrates. is dramatically improved. In addition, in FIG. 4, a substrate 6 with a window hole is used which is superimposed on the ceramic insulating substrate 1, and by limiting the spraying area of fired ceramic particles inside the window hole 7, uniform dispersion in a predetermined area is facilitated. An example is shown below. Examples of the present invention will be described below. (Example) Example 1 12 parts by weight of butyral resin and 100 parts by weight of 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. 6 parts by weight of DBP was added and mixed in an organic solvent to form a slurry, and a green sheet 8 with a thickness of 1 mm and a green sheet 9 with a thickness of 0.2 mm were made in the shapes shown in Figures 5 and 6 using a doctor blade. .
On the surface of the green sheet 8, a heating resistor pattern 10 and an electrode pattern 11a having the shape shown in FIG.
11b is thickly printed with platinum paste, and platinum lead wires 12a, 12b with a diameter of 0.3 mm are attached to the ends of each pattern.
and 12c were placed. On the other hand, green sheet 9
After punching out openings 13 at positions where the tips of the electrode patterns 11a and 11b can be exposed when stacked on the green sheet 21, these two green sheets 8 and 9 are laminated and thermocompressed. did. Separately, 4 parts by weight of polyvinyl alcohol was added to a powder having the same composition as the mixed powder used for each green sheet 8, 9, wet-mixed, granulated using a spray dryer, and then sieved into the particle size range shown in Table 1. Granules to be used as ceramic particles 2 were obtained. The granules are filled into the opening 5 so that the coverage ratio is approximately 1, and then the granules are held down with a pressure of 8 kg/cm ² at 50°C through a cushioning sheet, so that the granules are buried in the green sheet. I let it happen. Two green sheets 8 and 9 were then crimped together.
At the same time, it was fired in the air at a temperature of 1550°C and a holding time of 2 hours. The average burial depth of ceramic sintered particles 2 was approximately 1/10 of its average particle size. Next, 5 mol parts of platinum black was added to TiO ₂ powder with an average particle size of 1.2 μm, and 3 parts of platinum black was added to the total powder.
TiO ₂ mixed in butyl carbitol with the addition of parts by weight of ethyl cellulose and adjusted to a viscosity of 300 poise.
The paste was filled into the opening 5 and printed as a thick film so as to adhere to the tips of the electrode patterns 11a and 11b.
The gas sensor shown in FIG. 7 was prototyped by baking under conditions of a holding time of 1 hour. The test sensors No. 1 to 8 were distinguished according to the particle size range of the ceramic particles classified in Table 1. For comparison, gas sensor No. 1 is one in which the detection element 13 is formed without filling the opening 5 with ceramic particles. When the internal resistance of gas sensors No. 1 to No. 8 was measured in an atmosphere set at a temperature of 350℃ using a propane burner, they were all 20MΩ at the stoichiometric air-fuel ratio λ>1.
However, 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 discharged from a 2000 c.c. engine under full load for 5 minutes and then idling for 5 minutes until the detection element 13 peeled off. Table 1 also shows the results of time measurements.

[Table] Shows the values measured in.
As can be seen from Table 1, gas sensors No. 3 to No. 6 according to the present invention had extremely high peel strength compared to gas sensors No. 1 to No. 2 of the comparative example.
Although Comparative Example Gas Sensors No. 7 to No. 8 showed adhesive strength comparable to No. 3 to No. 6, the printing condition of the detection element 13 was uneven and there were many variations in resistance value. Example 2 Using the ceramic particles in sensor No. 4 of Example 1, the average burial depth (n = 5) after holding the granules with a cushion sheet and firing them under the conditions shown in Table 2, and this Ceramic insulation base JIS
Table 2 shows the results of measuring the dropout rate of the granules after the impact test specified in B8031-1974.

[Table] As shown in Table 2, particles with a small amount of buried particles are 1/20 to 1/20, although a large amount of particles have fallen off.
4 (5 to 25%), good density was obtained. It was difficult to bury the granules more than 28% because a large amount of the granules were broken during pressurization.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the main parts of the ceramic substrate of the present invention, Fig. 2 is a comparison diagram of the ceramic substrate before and after roughening, and a contrast diagram of the uneven base according to the present invention, and Fig. 3 is an external view of the gas sensor. FIG. 4 is a sectional view of another example, and FIGS. 5 to 7 are manufacturing procedure diagrams of the gas sensor. DESCRIPTION OF SYMBOLS 1... Ceramic insulating base, 2... Ceramic fired particles, 3... Uneven base, 4... Baked thick film layer.

Claims (1)

[Claims] 1. The surface of the ceramic insulating substrate 1 is provided with a baked thick film 4 of metal oxides, and the surface of the ceramic insulating substrate 1 has an average grain size.
Two groups of fired ceramic particles with a maximum particle size of 5 μm or more and a maximum particle size of 500 μm or less are dispersed and coalesced in a ceramic insulating substrate 1 by 1/20 to 1/4 of the average particle size while being partially buried in the ceramic insulating substrate 1, and formed on the surface of the substrate 1. The metal oxidation method is characterized in that it has an uneven base 3, and on this uneven base 3, four baked thick films of metal oxides are formed filling the inside spaces between the uneven base 3. A ceramic substrate that supports a thick film.