JPS6128208B2 - - 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. Specifically, the temperature characteristics of this capacitor are related to improvements in tan δ and insulation resistance. 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, a polycrystalline ceramic semiconductor grain boundary insulated dielectric material has been developed as a dielectric material with excellent heat resistance and a very large permittivity, in which the grain boundaries of a ceramic semiconductor 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 slight change in capacitance, and the tan δ is 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 a tuner or the like, for example. 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 to 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 tanδ 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 objectives, the present inventors were able to improve the insulation resistance, tan δ, and temperature characteristics by adding a predetermined amount of ZrO ₂ to SrTiO ₃ , and also added a semiconductor accelerator. as
Nb ₂ O ₅ or Ta ₂ O is suitable, and SiO ₂ is suitable as a crystal growth promoter, and a capacitor whose dielectric material is a polycrystalline porcelain semiconductor grain-boundary insulated dielectric material obtained by sintering these is suitable. It was discovered that it exhibits excellent characteristics, and led to the completion of the present invention,
The main component is SrTiO ₃ and contains 0.05 to 5% by weight of at least one of Nb ₂ O ₅ and Ta ₂ O ₅ , and SiO ₂
The dielectric material is a semiconductor ceramic containing 0.02 to 1% by weight of ZrO 2 and 0.05 to 5% by weight of ZrO ₂ and whose 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 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 and the resistance values are almost the same. 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 particle size increases to 10 μm or more from the vicinity where the amount of SiO ₂ is 0.02% by weight, and the BL
It is large enough to be used as a capacitor.
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. 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 glass and performing secondary firing in air. However, with this alone, it is difficult to obtain a capacitor with a small capacitance temperature characteristic, a small tan δ, and a large insulation resistance. Therefore, in the present invention, ZrO ₂ is further added. The addition of ZrO ₂ improves the temperature characteristics and tan
δ, is effective in improving insulation resistance. 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 ZrO ₂ to produce a BL capacitor, and then changed the amount _of ZrO ₂ added. When the changes in various properties were investigated, the results shown in Figure 3 were obtained. First, FIG. 3a shows the relationship between the amount of ZrO ₂ added and tan δ. As can be seen from FIG. 3a, the value of tan δ is about 1.4 without ZrO ₂ added, but when ZrO ₂ is added at about 0.1% by weight, it becomes the smallest value of about 0.5. And beyond this,
The value of tanδ gradually increases as the amount of ZrO ₂ added increases. Note that tanδ is the measurement frequency
Measurements were made using the bridge method under the conditions of 1kHz and measurement voltage of 1V. Further, FIG. 3c shows the relationship between the amount of ZrO ₂ 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 ZrO ₂ added increases, and at 1% by weight or more, the insulation resistance reaches 5×10 ¹⁰ Ω·cm or more. Furthermore, FIG. 3d shows the amount of ZrO ₂ added and the rate of change in capacitance with temperature. Here, the above temperature change rate is 20℃ based on the capacitance value at 20℃.
Measured in the range of ~80°C. From FIG. 3d, it can be seen that the rate of temperature change decreases as ZrO ₂ is added, and at about 5% by weight, the rate of temperature change becomes extremely small, about -2%. As mentioned above, the addition of ZrO ₂ was found to be extremely effective in improving the insulation resistance, tan δ, and capacitance of dielectrics containing SrTiO ₃ as the main component, but if added in excess, , tan δ increased on the contrary, and as shown in FIG. 3b, it was also found that the dielectric constant decreased. Therefore, the amount of ZrO ₂ added is preferably within the range of 0.05 to 5% by weight based on SrTiO ₃ . By setting it within such a range, the temperature characteristics of insulation resistance, tan δ, and capacitance are improved, and the dielectric constant is also ensured. 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, extremely high purity of raw materials 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 1.0% by weight of ZrO ₂ based on SrTiO ₃ was mixed and dried using a normal ceramic manufacturing method, and PVA was added to the powder.
A binder such as (polyvinyl alcohol) was added thereto 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 of Bi ₂ O ₃ , 10% by weight of B ₂ O ₃ , and PbO40.
% by weight of glass powder 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=28,500, tanδ=0.55%, insulation resistance=
2×10 ¹⁰ Ω・cm, temperature coefficient of capacitance is 20℃~80
It was -7.0% at °C. Note that tanδ 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 PVA was added to a powder that was mixed and dried using ordinary ceramic manufacturing means with a composition consisting of 0.1% by weight of Ta ₂ O ₅ , 0.4% by weight of SiO ₂ and 2.0% by weight of ZrO ₂ based on SrTiO 3 .
A binder such as (polyvinyl alcohol) was added to form granules, which were then calcined at 1450° C. for 2 hours in an atmosphere containing 1% H ₂ in N ₂ gas. Hereinafter, a BL capacitor was created in the same manner as in Example 1, and the characteristics of this capacitor were ε
= 12,000, tanδ = 0.8%, insulation resistance = 6 × 10 ¹⁰
Ω． cm, and the temperature coefficient was -3.0% from 20°C to 80°C. Example ₃ A composition consisting of 1.0% by weight of TaO ₅ , 0.6% by weight of SiO ₂ and 3.0% by weight of ZrO ₂ based on SrTiO 3 was mixed and dried using a normal ceramic manufacturing method, and PVA was added to the powder.
A binder such as (polyvinyl alcohol) was added to form granules, which were then calcined 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=25,000, tanδ=0.8%, insulation resistance=3×10 ¹⁰
The temperature coefficient was -4.0% from 20°C to 80°C. Example 4 A BL capacitor was prepared in the same manner as in Example ₁ by adding Nb ₂ O ₅ , SiO ₂ and ZrO ₂ to SrTiO 3 in the proportions shown in Table 1. 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 ZrO ₂ , the insulation resistance of the resulting polycrystalline ceramic semiconductor grain-boundary insulated dielectric material is greatly improved, the temperature change rate of capacitance becomes extremely small, and tanδ is also reduced. do. 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 a graph showing the relationship between the amount of ZrO ₂ added and various properties. It is a graph showing a relationship.

Claims (1)

[Claims] 1 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
A semiconductor porcelain grain boundary insulated capacitor whose dielectric material is semiconductor porcelain containing 0.02 to 1% by weight of SiO ₂ and 0.05 to 5% by weight of ZrO ₂ and whose grain boundary layer is made into an insulator.