JPH0380325B2 - - 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, if a current exceeding a certain limit is applied to the element due to a surge or the like, this semiconductor ceramic capacitor may be destroyed or may no longer function as a capacitor. 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 function 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-mentioned objects, the present invention has the following features:
SrTiO ₃ and metal oxides for promoting semiconductor formation
A voltage-dependent nonlinear resistor ceramic composition containing Dy ₂ O ₃ and a predetermined amount of at least one element selected from the group consisting of Ga, Pt, Tl, Al, Si, Be, and Li. This is what we propose. DESCRIPTION OF EMBODIMENTS The present invention will be specifically described below with reference to Examples. Example 1 SrTiO ₃ , Dy ₂ O ₃ and Ga ₂ O ₃ were weighed so as to have the composition ratio shown in Table 1 below, and then wet mixed using a ball mill or the like for 6 hours, 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 8 wt% of an organic binder (e.g., polyvinyl alcohol) was added and granulated, and then granulated with a press pressure of 1.0 t/cm ² into a shape of 8.0 mmφ x 1.0 mmt.
Pressure molded. This molded body is heated to 1 _{to 6}
Baked for an hour. The specific resistance of the fired body thus obtained was 0.1 to 0.8 Ω·cm, and the average particle size was 20 to 50 μm. Next, this fired body is heated at 1000 to 1300℃ in air.
The sintered body 4 shown in FIG. 3 was obtained by firing for 0.5 to 5 hours.
Further, both surfaces of the sintered body 4 were polished with an abrasive such as SiC, and electrodes 5 and 6 were formed using a conductive metal such as Ag. The diameter of the above electrodes 5 and 6 is 5.0mm
It was set as 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 varistor voltage per unit thickness (hereinafter referred to as V _1nA /mm) when a varistor current of 1mA flows, and α = 1/log (V _10nA /V1mA) [However, V _10nA
Characteristics as a varistor are evaluated based on the value of varistor voltage (V1nA is the varistor voltage when a varistor current of 10mA is applied and _V1nA is the varistor voltage when a varistor current of 1mA 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 Dy ₂ O ₃ 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, if Dy ₂ O ₃
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. During firing, Da ₂ O ₃ segregates at the grain boundaries of crystals mainly composed of SrTiO ₃ , 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 Ga ₂ O ₃ added is 0.005 mol % or more. Also,
When the amount of Ga 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 Dy ₂ O ₃ is less than 0.005 mol % because the specific resistance of the sintered body is large. moreover,
Since the specific resistance of the sintered body increases as the total amount of Dy ₂ O ₃ and Ga ₂ O ₃ added increases, V _1nA /mm generally takes a large value. 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 Ga ₂ O ₃ . Example 2 SrTiO ₃ , Dy ₂ O ₃ and SiO ₂ were mixed in the composition ratio shown in Table 2 below, mixed and molded and fired in the same manner as in Example 1, and measured under the same conditions. are shown in Table 2.

【table】

[Table] *……Comparative example The amount of Dy ₂ O ₃ shown in Table 2 is 0.005 to 10.000.
It contributes to lowering the specific resistance of the sintered body within the range of mol %, and can be used as a varistor by re-firing in air. SiO ₂ 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 SiO ₂ added is 0.005 mol % or more. Furthermore, when the amount of SiO ₂ 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) takes a large value when Dy ₂ O ₃ is less than 0.005 mol % because the specific resistance of the sintered body is large. Further, as the total amount of Dy ₂ O ₃ and SiO ₂ added increases, the specific resistance of the sintered body increases, so V _1nA /mm generally takes a large value. 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 % of Dy ₂ O ₃ and 0.005 to 10.000 mol % of SiO ₂ . In addition, in Examples 1 and 2, the case where only Ga ₂ O ₃ and SiO ₂ were used alone was explained, but instead of these, oxides of Pt, Tl, Al, Be, and Li were each used individually in the above specified amounts. It was confirmed that similar effects can be obtained even when used within the range of . It has also been found that similar effects can be obtained by using two or more of these oxides of Ga, Si, Pt, Tl, Al, Be, and Li, with the total addition amount falling within the specified amount range above. confirmed. 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.
This can be extended 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 _Dy2O3 as a metal oxide for promoting semiconductor formation, selected from the group consisting of Ga, Pt, Tl, Al, Si, Be, and Li. A voltage-dependent nonlinear resistor ceramic composition containing 0.005 to 10.000 mol% of at least one element in the form of an oxide.