JPH0380326B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention has a voltage dependence property suitable for making voltage dependent nonlinear resistors (hereinafter referred to as varistors) used for abnormal voltage absorption and noise removal in various electrical and electronic devices. The present invention relates to a non-linear resistor ceramic composition. Conventional configurations and their problems Traditionally, various electrical and electronic devices have been used to absorb abnormally high voltages (hereinafter referred to as surges), remove noise,
SiC varistors and ZnO-based varistors, which have voltage-dependent nonlinear resistance characteristics, were used to eliminate sparks. The voltage-current characteristics of such a varistor can be approximately expressed as follows. I=(V/C) Here, I is current, V is voltage, C is a constant specific to the varistor, and α is a voltage nonlinear index. The α of SiC varistors is about 2 to 7, and the α of some ZnO-based varistors is as high as 50. Although such varistors have excellent performance in absorbing relatively high voltages such as surges, their low dielectric constant and small specific capacitance prevent them from absorbing low voltages below the varistor voltage (e.g. noise, etc.). ), and the dielectric loss angle (tanδ) is 5.
~10%, which is large. On the other hand, in order to eliminate these noises, semiconductor porcelain capacitors with an apparent permittivity of about 5×10 ⁴ to 6×10 ⁴ and a tan δ of around 1% can be used by appropriately selecting the composition and firing conditions. ing. However, this semiconductor ceramic capacitor may break down or cease to function as a capacitor if a current exceeding a certain level is applied to the element due to a surge or the like. For the reasons mentioned above, in electrical and electronic equipment, varistors are usually used in combination with capacitors and other parts (e.g. coils) for purposes such as surge absorption and noise removal.For example, noise filters are It is structured like this. Figure 1 shows a general conventional noise filter circuit, and Figure 2 shows a conventional noise filter circuit configured by combining a varistor, a capacitor, and a coil, where 1 is a coil, 2 is a capacitor, and 3 is a I'm a barista. However, the configuration shown in FIG. 2 has the disadvantage that the number of parts inside the device increases and it is contrary to the trend toward miniaturization of devices. Purpose of the Invention The present invention eliminates the drawbacks of conventional surge absorption and noise removal as described above, and provides a composite device that has the functions of both a varistor and a capacitor and can perform surge absorption and noise removal with a single element. The object of the present invention is to provide a porcelain composition suitable for making a varistor having a porcelain composition. Structure of the Invention In order to achieve the above objects, the present invention has the following features:
SrTiO ₃ and metal oxides for promoting semiconductor formation
Ta ₂ O ₅ and Eu, Gd, Tb, Tm, Lu, Th, Ir,
The present invention proposes a voltage-dependent nonlinear resistor ceramic composition containing a predetermined amount of at least one element selected from the group consisting of Os, Hf, and Ru. DESCRIPTION OF EMBODIMENTS The present invention will be specifically described below with reference to Examples. Example 1 SrTiO ₃ , Ta ₂ O ₅ and Gd ₂ O ₃ were weighed to have the composition ratio shown in Table 1 below, mixed wet for 6 hours using a ball mill, etc., dried, and then
Calcinate in air at 1000-1250℃ for 1-5 hours. After that, it was wet-pulverized for 4 hours using a ball mill, etc., dried, and then granulated by adding 8wt% of an organic binder (e.g. polyvinyl alcohol).
Pressure molded at 1.0t/cm ² . This molded body is heated to 1300 to 1450°C in a reducing atmosphere (for example, N ₂ :H ₂ =10:1).
It was baked for 1 to 6 hours. The specific resistance of the fired body thus obtained is 0.1~0.8Ω・cm, and the average particle size is 20~0.8Ω・cm.
It was 50μm. Next, this fired body is placed in the air.
Firing was performed at 1000 to 1300°C for 0.5 to 5 hours to obtain the sintered body 4 shown in FIG. Furthermore, both planes of the sintered body 4 are
After polishing with an abrasive such as SiC, electrodes 5 and 6 were formed using a conductive metal such as Ag. The above electrodes 5, 6
The diameter was 5.0 (mm)φ. The characteristics of the device thus obtained are also shown in Table 1.

【table】

[Table] *... Comparative example Here, the characteristics of the element as a varistor are evaluated using the voltage-current characteristic equation described above: I = (V/C) This can be done by α and c in a constant (α is a non-linear index). However, since accurate measurement of C is difficult, in the present invention,
The value of the varistor voltage per unit thickness (hereinafter referred to as V _1nA /mm) when a varistor current of 1mA flows,
α=1/log (V _10nA /V _1nA ) [However, V _10nA is
The characteristics of the varistor are evaluated based on the value of the varistor voltage when a varistor current of 10 mA is applied, and V _1nA is the varistor voltage when a varistor current of 1 mA is applied. In addition, the characteristics as a capacitor are evaluated using the dielectric constant ε and dielectric loss angle tan δ at a measurement frequency of 1 KHz. The above data shows the firing temperature and time in a reducing atmosphere at 1400℃ for 2 hours.
The firing temperature and time were 1200°C and 3 hours in air. As shown in Table 1, the amount of Ta ₂ O ₅ added is 0.005.
If it exceeds mol%, it will form a solid solution in the crystal lattice mainly composed of SrTiO ₃ during sintering, and the specific resistance of the sintered body can be lowered to around 1.0 Ω cm by controlling the valence, so re-sintering in air is possible. By doing so, it can be used as a varistor. However, Ta ₂ O ₅
If it exceeds 10.000 mol%, it will no longer form a solid solution.
The specific resistance of the sintered body increases, making it unsuitable for use as a varistor. Gd ₂ O ₃ segregates at the grain boundaries of crystals mainly composed of SrTiO ₃ during firing, increases the resistivity of the grain boundary layer, and contributes to increasing the nonlinearity of the sintered body. Such an effect appears when the amount of Gd ₂ O ₃ added is 0.005 mol % or more. Also,
When the amount of Gd ₂ O ₃ added exceeds 10.000 mol %, the dielectric loss angle tan δ increases, the dielectric constant ε gradually decreases, and the nonlinear index α also decreases. Also, the varistor voltage per unit thickness (V _1nA /
mm) becomes a large value when Ta ₂ O ₅ is less than 0.005 mol % because the specific resistance of the sintered body is large. Therefore, the range that satisfies both the functions of a varistor and a capacitor at the same time is 0.005 to 10.000 mol% for Dy ₂ O ₃ and 0.005 to 10.000 mol % for La ₂ O ₃ . In addition, in the example, the case where only Gd ₂ O ₃ was used alone was explained, but instead of this, Eu,
It has been confirmed that similar effects can be obtained even when oxides of Tb, Tm, Lu, Th, Ir, Os, Hf, and Ru are used alone in the above-mentioned prescribed amounts. In addition, these Gd, Eu, Tb, Tm, Lu, Th, Ir, Os, Hf,
It has been confirmed that similar effects can be obtained even when two or more types of Ru oxides are used in a total amount within the predetermined range described above. Using the above elements, we created a circuit as shown in Figure 4, and investigated the output status for noise input A as shown in Figure 5. As a result, we found that the output status curve B in Figure 5 shows I was able to suppress the noise.
In FIG. 5, 7 is an element of the present invention, and 8 is a coil. Note that the output condition of the conventional filter circuit shown in FIG. 1 is as shown by the output condition curve C in FIG. 5, and noise is not removed sufficiently. Further, the conventional filter circuit including the varistor shown in FIG. 2 can obtain an effect similar to the circuit shown in FIG. . Effects of the Invention As described above, the device using the ceramic composition according to the present invention has an unprecedented composite function, and can play the roles of a varistor and a capacitor at the same time. It simplifies, contributes to compactness, high performance, and low cost, and is useful for absorbing surges in various electrical and electronic devices.
The application can be expanded to noise removal, and its practical value is extremely large.

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing conventional noise filter circuits, FIG. 3 is a cross-sectional view of an element using the ceramic composition of the present invention, and FIG. 4 is a noise filter using the element shown in FIG. 3. FIG. 5 is a circuit diagram showing a filter circuit, and is a characteristic diagram showing the input noise and output noise situations of the present invention and the conventional noise filter circuit.

Claims (1)

[Claims] 1 80.000 to 99.990 mol% of _SrTiO3 , _0.005 to 10.000 mol% of _Ta2O5 as a metal oxide for promoting semiconductor formation, Eu, Gd, Tb, Tm, Lu, Th, Ir, Os,
At least one selected from the group consisting of Hf, Ru
0.005~ in the form of oxides of more than one kind of elements
A voltage-dependent nonlinear resistor ceramic composition characterized by containing 10.000 mol%.