JPS6128209B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a semiconductor porcelain grain boundary insulated capacitor whose dielectric is a sintered body mainly composed of strontium titanate, and in particular relates to improvements in the temperature characteristics, tan δ, and insulation resistance of this capacitor. It is something. In general, dielectric materials for capacitors etc.
Plastic films such as Mylar film are used, which are easily available, but they have poor heat resistance and burn, so there is a problem that the range of use is limited due to the increase in heat generation due to the increase in electric power. . Therefore, in recent years, polycrystalline porcelain semiconductor grain boundary insulated dielectrics have been developed as dielectrics with excellent heat resistance and extremely high permittivity, in which the grain boundaries of magnetic semiconductors are selectively insulated. Semiconductor porcelain grain boundary insulated capacitors (BL capacitors) using dielectric materials are available. As this type of dielectric material, for example, barium titanate (BaTiO ₃ ) type is known, and a BL capacitor using this has a
A dielectric constant of about 100% has been achieved. However, this
For BL capacitors, the temperature change is approximately ±40% of the value at 20°C in the range of -30°C to +85°C.
There is a change in capacitance of about 5%, and tan δ is also about 5
Its usefulness as a capacitor was limited due to its relatively large size of ~10%. That is,
This temperature change in capacitance causes frequency characteristics to change depending on the temperature when used in, for example, a tuner. On the other hand, as the above-mentioned dielectric material, a material mainly composed of strontium titanate (SrTiO ₃ ) is also known, and a BL capacitor using this material has also been proposed. This kind of capacitance change due to temperature change is as low as about ±15%, and tan δ is also 2.
Since it is as low as ~5%, it can be said to be superior to BaTiO ₃ series BL capacitors. However, this SrTiO ₃ -based BL capacitor is significantly inferior in terms of insulation resistance and tan δ compared to mylar film capacitors, which are thought to compete in practical terms. Therefore, the present invention was proposed in view of the above circumstances, and has a small temperature change in capacitance.
Another object of the present invention is to provide a semiconductor porcelain grain boundary insulated capacitor that has excellent insulation resistance and tan δ and has a high dielectric constant. As a result of intensive research to achieve the above-mentioned purpose, the present inventors have found that by adding a predetermined amount of BaTiO ₃ to SrTiO ₃ , it is possible to improve insulation resistance, tan δ, and temperature characteristics, and further promote semiconductorization. as an agent
A capacitor whose dielectric material is a polycrystalline porcelain semiconductor grain-boundary insulated dielectric material obtained by sintering Nb ₂ O ₅ or Ta ₂ O ₅ , and SiO ₂ as a crystal growth promoter. The present invention was completed by discovering that the compound exhibits excellent characteristics,
Mainly composed of SrTiO ₃ and containing 0.05 to 5% by weight of at least one of Nb ₂ O ₅ and Ta ₂ O ₅
0.02-1% by weight of _SiO2 and 0.5-20% by weight of _BaTiO3
It is characterized in that the dielectric material is semiconductor porcelain in which the grain boundary layer is made into an insulator. In order to obtain a polycrystalline ceramic semiconductor grain boundary insulated dielectric material mainly composed of SrTiO ₃ , this SrTiO ₃
It is necessary to promote the conversion of SrTiO 3 into a semiconductor and grow ceramic semiconductor particles, but when the present inventors added various impurities to SrTiO ₃ and fired it in a reducing atmosphere containing H ₂ , Nb ₂ O ₅ and It was found that metal oxides such as Ta ₂ O ₅ particularly promote semiconductor formation. For example, add Nb ₂ O ₅ to SrTiO ₃ and add 1% H ₂
When firing was performed at 1400° C. for 2 hours in an atmosphere containing N ₂ gas, the resistance value changed as shown in FIG. 1 depending on the amount added. That is, Nb ₂ O ₅ is replaced by SrTiO ₃
When 0.05% by weight of SrTiO 3 was added, the low resistance value suddenly decreased, and SrTiO ₃ became significantly semiconducting.
In particular, when the amount of Nb ₂ O ₅ added exceeds 1% by weight, the effect of semiconductor formation is saturated, resulting in almost the same low resistance value. This tendency was the same when Ta ₂ O ₅ was added instead of Nb ₂ O ₅ . However, Nb ₂ O ₅ and
If the amount of Ta ₂ O ₅ added exceeds 5% by weight, the sinterability becomes extremely poor, making it unsuitable for use in capacitors. Therefore, the amount of Nb ₂ O ₅ and Ta ₂ O ₅ added is preferably within the range of 0.05 to 5% by weight based on SrTiO ₃ . The amount added above is 0.05% by weight
If it is less than that, SrTiO ₃ cannot be sufficiently converted into a semiconductor. On the other hand, if the amount added exceeds 5% by weight, the sinterability will be extremely poor and it will be difficult to produce a dielectric. In order to insulate only the crystal grain boundaries of the semiconductor-converted particles in this manner, the crystal particles need to be large and uniform. If the crystal grains are too small, the inside of the crystal will be insulated during insulation, resulting in a decrease in dielectric constant. Therefore, it is necessary to further add a crystal growth promoter to SrTiO ₃ , and it has been found that among these crystal growth promoters, SiO ₂ particularly significantly promotes crystal growth. Figure 2 shows the relationship between the amount of SiO ₂ and the crystal grain size when fired at 1400°C for 2 hours in a reducing atmosphere. From this figure 2, the amount of SiO ₂ is 0.02% by weight.
The particle size increases from around 10 μm or more, which is large enough to be used in BL capacitors. However, if it exceeds 1% by weight, the particle size becomes too large and there is a possibility that particles exceeding the thickness of a normal capacitor (approximately 0.4 mm) will appear, which is not preferable. In addition, the strength of the particles also becomes weaker. As described above, a predetermined amount of Nb ₂ O ₅ or Ta ₂ O ₅ and SiO ₂ are added to SrTiO ₃ and primary firing is performed in a reducing atmosphere containing H ₂ to form a B ₂ O ₃ -Bi ₂ O ₃ system. or PbO—
A BL capacitor with a high dielectric constant can be obtained by applying B ₂ O ₃ -Bi ₂ O ₃ glass and performing secondary firing in air. However, with this alone, it is difficult to obtain a capacitor with a small temperature characteristic of capacitance, a small tan δ, and a large insulation resistance. Therefore, we conducted further experiments to improve these characteristics. At room temperature, capacitance varies with temperature.
It is known that SrTiO ₃ has a negative relationship and BaTiO ₃ has a positive relationship. Therefore, the present inventor proposed that if a part of Sr in SrTiO ₃ is replaced with Ba,
We thought that we would be able to obtain a temperature characteristic close to zero. From this point of view, the present inventors added 1% by weight of Nb ₂ O ₅ and 0.5% by weight of SiO ₂ to SrTiO ₃ and further added BaTiO ₃ to produce _a BL capacitor. When the changes in various properties were investigated by changing the amount added, the results shown in FIG. 3 were obtained. First, Figure 3a shows the amount of BaTiO ₃ added and tan δ
It shows the relationship that BaTiO ₃ is 1% by weight ~
A range of 20% by weight is sufficient for practical use. In addition,
tan δ was measured by the bridge method under the conditions of a measurement frequency of 1 kHz and a measurement voltage of 1 V. Further, FIG. 3c shows the relationship between the amount of BaTiO ₃ added and the insulation resistance. Note that this insulation resistance was measured after applying DC 100V for 1 minute. From FIG. 3c, it can be seen that the insulation resistance increases rapidly as the amount of BaTiO ₃ added increases, and at 10 to 15% by weight, the insulation resistance reaches about 10 ¹³ Ω·cm. However, if it exceeds 20% by weight, it will deteriorate again. Furthermore, FIG. 3d shows the amount of BaTiO ₃ added and the rate of change in capacitance with temperature. Here, the temperature change rate above is 20°C based on the capacitance value at 20°C.
It was measured in the range of ℃ to 80℃. From FIG. 3d, it can be seen that the rate of temperature change shifts in the positive direction as BaTiO ₃ is added, and a material with a zero temperature coefficient can be obtained at about 10% by weight. As mentioned above, the addition of BaTiO ₃ above can lead to SrTiO ₃
It has been found that it is extremely effective in improving the insulation resistance, tan δ, and capacitance of dielectrics whose main components are temperature changes; however, when added in excess, tan δ increases, and furthermore, as shown in Figure 3. As shown in b, it was also found that the dielectric constant decreased. Therefore, the above amount of BaTiO ₃ added is equal to SrTiO ₃
It is preferably within the range of 0.5 to 20% by weight. By setting this range,
The temperature characteristics of insulation resistance, tan δ, and capacitance are improved, and the dielectric constant is also secured. By the way, when producing the above-mentioned dielectric, it is necessary to pay attention to the purity properties of the raw materials. Generally, TiO ₂ and SrCO ₃ are used to make SrTiO ₃ , but here there are two types of TiO ₂ : anatase type and rutile type. The anatas type has better sinterability, but the rutile type has better dielectric constant. . In addition, both contain Fe ₂ O ₃ as an impurity, but care must be taken because this Fe ₂ O ₃ interferes with semiconductor formation and causes deterioration of insulation properties. SrCO ₃ is mainly BaCO ₃ and
Contains CaCO ₃ as an impurity, which causes variations in the temperature characteristics of the dielectric constant. Also,
Depending on the manufacturing method, TiCO ₃ also contains Na components, which has a significant effect on sinterability and insulation properties. however,
Increasing the purity of the raw material to an extremely high degree is not preferable in terms of sinterability. This is because trace amounts of impurities play an important role in sintering. When carrying out the present invention, raw materials should be prepared keeping this in mind. Next, specific examples of the present invention will be described. Example 1 A composition consisting of 0.8% by weight _of Ta ₂ O ₅ , 0.4% by weight of SiO ₂ and 10% by weight of BaTiO _{3 based on SrTiO 3} was mixed and dried into a powder using a normal ceramic manufacturing method.
A binder such as PVA (polyvinyl alcohol) was added to form granules, which were then fired at 1450° C. for 2 hours in an atmosphere containing 1% H ₂ in N ₂ gas. Add to this 50% by weight Bi ₂ O ₃ , 10% by weight B ₂ O ₃ and PbO
Glass powder consisting of 40% by weight was applied with a brush and baked in air at 1180℃ for 2 hours to bake the silver electrode.
I created a BL capacitor. The characteristics of this capacitor are: ε=14000, tan δ=0.35%, insulation resistance=
7×10 ¹² Ω・cm, temperature coefficient of capacitance is 20℃~80
It was 0% at ℃. Note that tan δ and capacitance are based on Automatic Capacitance Bridge (product name: YHP).
4270A), measurement frequency 1kHz, measurement voltage 1V
Measured under the following conditions. (The same applies hereinafter.) Example 2 A composition consisting of 0.1% by weight of Ta ₂ O ₅ , 0.4% by weight of SiO ₂ and 10% by weight of BaTiO ₃ based on SrTiO ₃ was mixed and dried into powder using a normal ceramic manufacturing method.
Bingu such as PVA (polyvinyl alcohol) is added and formed into granules, which are then mixed with 1 H ₂ in N ₂ gas.
It was baked at 1,450°C for 2 hours in an atmosphere containing %. Hereinafter, a BL capacitor was produced in the same manner as in Example 1 above. The characteristics of this capacitor are
ε=7000, tan δ=0.3%, insulation resistance=10×10 ¹²
The temperature coefficient was +1.3% from 20°C to 80°C. Example ₃ A composition consisting of 1.0% by weight of Ta ₂ O ₅ , 0.6% by weight of SiO ₂ and 10% by weight of BaTiO ₃ based on SrTiO 3 was mixed and dried into powder using a normal ceramic manufacturing method.
A binder such as PVA (polyvinyl alcohol) was added to form granules, which were then fired at 1450° C. for 2 hours in an atmosphere containing 1% H ₂ in N ₂ gas. Hereinafter, a BL capacitor was produced in the same manner as in Example 1 above. The characteristics of this capacitor are
ε=20000, tan δ=0.45%, insulation resistance=3×
10 ¹² Ω·cm, and the temperature coefficient was 0% from 20°C to 80°C. Example 4 Nb ₂ O ₅ , SiO ₂ and BaTiO 3 were added to SrTiO ₃ in the proportions shown in Table 1, and the same procedure as described in Example 1 was carried out _.
A BL capacitor was created using the same method.
The characteristics of each capacitor were as shown in Table 2.

【table】

[Table] As is clear from the above description, by applying the present invention, it is possible to obtain a capacitor with characteristics far superior to that of conventional BL capacitors. In other words, by adding BaTiO ₃ , the insulation resistance of the resulting polycrystalline semiconductor grain boundary insulated dielectric material is greatly improved, the temperature change rate of capacitance becomes extremely small, and tan δ also decreases. descend. Further, by adding Nb ₂ O ₅ or Ta ₂ O ₅ and adding SiO ₂ , semiconductor formation and crystal growth are promoted, and the dielectric constant becomes large. Therefore, by using this polycrystalline ceramic semiconductor grain boundary insulated dielectric as a dielectric,
It is possible to obtain a semiconductor porcelain grain boundary insulated capacitor which has excellent heat resistance and whose filter frequency characteristics do not change due to changes in temperature when used in a tuner, for example.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the amount of Nb ₂ O ₅ added and semiconductor formation, Figure 2 is a graph showing the relationship between the amount of SiO ₂ added and average grain size, and Figure 3 is the amount of BaTiO ₃ added and various characteristics. It is a graph showing the relationship between.

Claims (1)

[Claims] 1 SrTiO ₃ as the main component, containing 0.05 to 5% by weight of at least one of Nb ₂ O ₅ and Ta ₂ O ₅ , and 0.02 to 1% by weight of SiO ₂ and 0.5 to 20% by weight of BaTiO ₃ A semiconductor porcelain grain boundary insulated capacitor whose dielectric material is semiconductor porcelain with an insulating grain boundary layer.