JPS6115529B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a reduced type semiconductor ceramic composition based on barium titanate. Semiconductor porcelain capacitors are generally divided into two types: a grain boundary type that uses the grain boundaries of porcelain, a weir layer type that uses the surface of porcelain, and a reduced type (also called a reoxidation type).
There are a wide variety of manufacturing methods depending on the purpose and application. Reduced semiconductor porcelain capacitors are usually obtained by heat-treating dielectric porcelain in a reducing atmosphere, applying a silver paste for electrodes to the semiconductor porcelain, and then heat-treating it. A thin dielectric layer is formed between the silver electrodes. The capacitance, insulation resistance, breakdown voltage, and other electrical properties of the capacitor depend on the properties of this thin dielectric layer. In reduction type semiconductor ceramic capacitors, when the capacitance per unit area is increased, the dielectric layer becomes thinner and the wave breakdown voltage inevitably decreases.On the other hand, when trying to increase the breakdown voltage, the dielectric layer becomes thicker and the dielectric layer becomes thinner. It has the property of decreasing the capacity of . Further, the temperature characteristic of the capacitance of this dielectric layer appears as the temperature characteristic of the capacitance of the reduced semiconductor ceramic capacitor, and is extremely similar to the temperature characteristic curve of the dielectric ceramic before reduction. In other words, it is presumed that this thin dielectric layer was formed when the surface of the semiconductor ceramic obtained by reduction was oxidized again during the heat treatment during electrode formation, and it is largely influenced by the temperature characteristics or dielectric constant of the dielectric ceramic. It is something that will be done. Furthermore, in order to form a thin and uniform dielectric layer on the semiconductor ceramic surface, it is necessary that the dielectric ceramic surface be homogeneous and composed of particles of several μm or less. In this way, the change in capacity due to temperature is small,
In order to obtain a reduced semiconductor ceramic capacitor that has a high breakdown voltage and a large capacity, it is necessary to have a large dielectric constant, a small change in dielectric constant with respect to temperature, and a ceramic surface consisting of homogeneous small particles of several micrometers or less. Semiconductor porcelain must be obtained that satisfies the following requirements: it is a dielectric porcelain, and the porcelain surface layer can be easily made thin and a homogeneous dielectric layer can be formed at the heat treatment temperature used when forming silver electrodes on the surface of the reduced porcelain. Must be. Semiconductor porcelain for reduction type semiconductor porcelain capacitors has been widely disclosed in patent publications and literature, and has been put into practical use, but semiconductor porcelain capacitors can be destroyed if the capacitance per unit area (μF/cm ² ) is increased. This had the disadvantage that the voltage value was small, which placed restrictions on its use. This is because the breakdown voltage and capacitance of a capacitor that forms a dielectric layer on the surface of semiconductor ceramics are related to the thickness of the dielectric layer that is formed.The thinner the thickness, the larger the capacitance, but the smaller the breakdown voltage. If the thickness of the dielectric layer is increased to increase the
The drawback was that the capacity was small. In the case of reduced semiconductor porcelain capacitors, the dielectric constant of the dielectric layer on the surface of the semiconductor porcelain is almost the same as that of sintered porcelain before reduction, so it is necessary to increase the thickness, increase the breakdown voltage value, and obtain large capacity. Naturally, then, the dielectric constant of the porcelain must be increased, but increasing the dielectric constant causes extremely poor temperature characteristics. The present invention eliminates the above-mentioned drawbacks, has a large capacity, has a high breakdown voltage value, has an extremely small change in capacitance with applied voltage, and has excellent temperature characteristics, and can be used in an expanded range of applications. The present invention provides a reduced semiconductor ceramic composition with excellent dielectric properties. That is, the present invention applies 0.01 to 0.3 wt to a composition containing 99.3 to 78.0 mol% _of BaTiO3, 0.1 to 5.0 mol% of _CeO2 , _0.1 to 2.0 mol% of _Bi2O3 , and 0.5 to 15.0 mol% _of ZrO2.
% Mn and 3.0wt% or less SiO ₂ are added to prepare the raw material mixture, which is formed into a plate shape and fired. The porcelain thus obtained is heated in a reducing atmosphere to become a semiconductor, an electrode is applied to the surface of this porcelain, and the porcelain is heated again in an oxidizing atmosphere to form an oxidizing thin layer between the semiconductor porcelain surface and the silver electrode. , a semiconductor ceramic capacitor was obtained. The reduced semiconductor porcelain composition of the present invention has an extremely small and uniform crystal grain size compared to conventional semiconductor porcelain, and has fewer pores inside the porcelain, so it has a much smaller and more uniform crystal grain size than conventional semiconductor porcelain. Decreasing the crystal grain size improves the capacitance-temperature characteristics, but decreases the dielectric constant, and therefore, when attempting to obtain a large capacity, the dielectric layer on the surface of the semiconductor ceramic becomes thinner, resulting in a lower breakdown voltage value. On the other hand, the semiconductor ceramic obtained from the reduced semiconductor ceramic composition of the present invention has a low dielectric constant despite having a small crystal grain size.
It is extremely large (more than 5000), has excellent temperature characteristics, and is easy to undergo ring formation, which is required for the ceramics of reduced semiconductor ceramic capacitors. It satisfies the conditions. Hereinafter, the present invention will be described in detail with reference to examples. When preparing the sample, as described in Table 1.
_BaTiO3 , _CeO2 , _{Bi2O3 , ZrO2MnCO3 and SiO2}
Weigh each to give the desired composition, and wet mix them in a polypot for about 16 hours. After mixing, the mixture is dehydrated and dried, and about 2.5 wt% of an organic binder such as polyvinyl alcohol is added, the particles are sized, and the mixture is formed into a disc with a diameter of 12.0 mm and a thickness of 0.6 mm under a pressure of 1000 Kg/cm ² . The formed disc is then fired at 1280-1360°C for 2 hours. The dielectric ceramic thus obtained is heat treated in a reducing atmosphere at 850° C. for 30 minutes to obtain semiconductor ceramic. Silver paste for electrodes was applied to this semiconductor porcelain, and heat treatment was performed for 30 minutes in an oxidizing atmosphere at 700 to 900°C to produce a reduced semiconductor porcelain capacitor. Table 1 shows the measurement results of capacitance, tan δ, insulation resistance, breakdown voltage, and voltage dependence of the capacitor manufactured by the above method. When measuring the sample, the capacitance and tan δ were measured at a frequency of 1 kHz and a voltage of 1 _Vrm9 , and the insulation resistance was measured after applying a voltage of 25 VDC for 60 seconds. In addition, the breakdown voltage is determined using a DC step-up method, and the capacitance changes depending on the reduction temperature and silver firing temperature.
It was kept constant at 0.1 μF/cm ² to facilitate comparison with other characteristics. Furthermore, in the voltage dependence (Co-C ₂₅ /C
The 0×100)% value is the capacitance change value when a voltage of 25 VDC is applied for 60 seconds.

[Table] In Table 1, sample numbers 2 to 4, 7, 8, 11,
12, 15, 16, 19, 20 are related to the present invention,
Sample numbers 1, 5, 6, 9, 10, 13, 14, 17, 18,
21 is outside the scope of the present invention for comparison. As is clear from Table 1, the compositional limitations of the reduced semiconductor ceramic composition of the present invention are as follows: (1) When Bi ₂ O ₃ is less than 0.1 mol %, the voltage dependence of the capacity and tan δ are large; %, it becomes difficult to sinter the porcelain, resulting in low insulation resistance and breakdown voltage. (2) When CeO ₂ is less than 0.1 mol%, the voltage dependence of tan δ and capacitance is high, and the insulation resistance and breakdown voltage are low. Moreover, if it exceeds 5.0 mol%, abnormal growth of crystals will occur, resulting in lower insulation resistance and breakdown voltage. (3) If ZrO ₂ is less than 0.5 mol%, sintering is insufficient, the dielectric constant is low, the insulation resistance and breakdown voltage are low, and the tan
δ is high. Moreover, if it exceeds 15 mol%, the crystal grain size becomes large, there are many pores inside the porcelain, and the insulation resistance and breakdown voltage are low. (4) Addition of SiO ₂ lowers the sintering temperature of porcelain, but if it exceeds 3.0wt%, fusion may occur in porcelain, making it unsuitable. (5) Furthermore, when the addition of Mn is less than 0.01wt%, insulation resistance and breakdown voltage are low, and tanδ is high. Also
If it exceeds 0.3wt%, the dielectric constant of sintered porcelain will be low;
The insulation resistance and breakdown voltage are low, and the voltage dependence of the capacitance is also large. Furthermore, Table 2 shows the results of a comparison between the porcelain composition of the present invention and conventional examples described in patent publications and literature.

Table 2 shows that the reduced semiconductor ceramic composition of the present invention is excellent in tan δ, insulation resistance, breakdown voltage, and various electrical properties. This is because the crystal grain size of the sintered porcelain is minute, as shown in Table 2, and is uniform, as reflected in the apparent specific gravity and porosity. Furthermore, although the amount of internal pores is small and the dielectric constant of sintered porcelain is high at over 5000, the temperature characteristic of capacitance is ±20°C in the temperature range of -25 to +85°C. It has excellent properties such as a good value of 30% or less. Table 3 also shows that in a composition equivalent to sample number 3 in the above example,
The results of checking the electrical properties of samples obtained by changing the sintering temperature are shown, and it can be seen that the temperature characteristics of the capacity depending on the sintering temperature are good. Therefore, since the temperature characteristics of the dielectric constant of the sintered porcelain and the temperature characteristics of the reduced semiconductor ceramic capacitor are exactly the same, process control regarding the temperature characteristics is easy.

[Table] As described above, BaTiO ₃ according to the present invention,
Sintered porcelain of a reduced type semiconductor porcelain composition characterized by adding Mn and SiO ₂ to the basic composition of Bi ₂ O ₃ , CeO ₂ , and ZrO ₂ is heated in a reducing atmosphere, and silver is added to the semiconducting semiconductor porcelain. Reduced semiconductor ceramic capacitors, which are obtained by applying paste and baking silver to form a dielectric layer on the semiconductor ceramic surface, have higher insulation resistance, breakdown voltage, and lower dielectric loss than conventional products. Furthermore, the capacitance changes little under high voltage, and its use under high voltage has been significantly expanded. Furthermore, since it has excellent stability in capacitance temperature characteristics and thermal shock resistance, it can be manufactured extremely easily and stably, and has great industrial value.

Claims (1)

[Claims] 1 _BaTiO3 99.3-78.0 mol%, _{Bi2O3 0.1-2.0} mol%, _CeO2 0.1-5.0 mol%, ZrO2 _0.5-15 mol%
A reduced semiconductor ceramic composition obtained by adding 0.01 to 0.3 wt% Mn and 3.0 wt% or less SiO ₂ to the composition.