JPS644646B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a voltage nonlinear resistor, and more particularly to a voltage nonlinear resistance ceramic mainly composed of zinc oxide (ZnO) used as an overvoltage protection element. Conventionally, silicon carbide (SiC) and
Pallisters whose main components are selenium (Se), silicon (Si), or ZnO are used. Among them, pallisters whose main component is ZnO generally have a low limiting voltage.
Because it has characteristics such as a large voltage non-linearity coefficient, it is suitable for overvoltage protection of equipment made of devices with low overcurrent tolerance such as semiconductor elements, so it can be used in place of SiC pallisters, etc. It has become widely used. In addition, voltage nonlinear resistance porcelain, which is manufactured by firing ZnO as a main component and adding neodymium (Nd) and cobalt (Co) as subcomponents in the form of elements or compounds, has excellent voltage nonlinearity. It is known that there are However, in such a voltage non-linear resistance ceramic, if the operation start voltage is significantly reduced due to a rise in ambient temperature, leakage current increases, and therefore there is a possibility of thermal runaway occurring.
Another drawback was that the limiting voltage was rather high.
Therefore, in practice, in addition to these excellent voltage nonlinearities, it is desirable that the operation start voltage be as stable as possible with respect to the ambient temperature and that the limiting voltage be as low as possible. Therefore, an object of the present invention is to provide a voltage nonlinear resistance ceramic that improves the stability of the operation start voltage with respect to ambient temperature, further reduces the limiting voltage, and has more suitable characteristics. . Therefore, the present inventors added cesium (Cs) and chromium (Cr) as subcomponents to the conventional voltage nonlinear resistance ceramic, which is made of ZnO as a main component and Nd and Co as subcomponents. We discovered that by adding this material, it is possible to obtain a voltage nonlinear resistance ceramic that maintains excellent voltage nonlinearity, improves the stability of the operation start voltage with respect to ambient temperature, and reduces the limiting voltage. sold the invention. Therefore, according to the present invention, there is provided a voltage nonlinear resistance porcelain containing ZnO as a main component and Nd and Co as subcomponents, and further containing Cs and Cr as subcomponents. is provided. According to a more preferred embodiment of the present invention, ZnO is the main component, and in addition to Nd and Co, Cs and Cr are used as subcomponents, Nd is 0.1 to 5.0 atomic%, Co is 0.5 to 5 atomic%, and Cs is 0.05 atomic%. ~0.5 at%, Cr 0.05-0.5 at%
A voltage non-linear resistance porcelain is provided comprising in an amount such that . Here, atomic % means the percentage of the number of atoms of the added metal element relative to the total number of atoms of each component metal element in the raw material composition blended to produce a predetermined voltage nonlinear resistance ceramic. . The voltage nonlinear resistance porcelain according to the present invention is generally
It is produced by firing and sintering a mixture of ZnO and additive metals or compounds at high temperatures in an oxygen-containing atmosphere. Usually, additive components are added in the form of metal oxides, but compounds that can become oxides during the firing process, such as carbonates, hydroxides, fluorides, etc., can also be used, or they can be used in the form of simple elements. It can also be converted into an oxide during the firing process. According to a particularly preferred method, the voltage nonlinear resistance porcelain of the present invention is produced by thoroughly mixing ZnO powder with powder of an additive metal or compound,
Calcinate at ~1000℃ for several hours, thoroughly crush the calcined product, mold it into a predetermined shape, and then heat it in air at ~1200℃.
It is manufactured by firing at a temperature of around 1400℃ for several hours. If the firing temperature is lower than 1200°C, sintering will be insufficient and the properties will be unstable. Furthermore, at temperatures higher than 1400°C, it becomes difficult to obtain a homogeneous sintered body, voltage nonlinearity decreases, and there are difficulties in reproducibility in controlling characteristics, making it difficult to obtain a product for practical use. Examples are now presented to further illustrate the invention. Example Nd ₂ O ₃ , Co ₃ O ₄ , Cs ₂ CO ₃ , Cr ₂ O ₃ powder was added to ZnO powder in an amount corresponding to the predetermined atomic % listed in Table 1 below and thoroughly mixed. After, 500~1000℃
I baked it for several hours. Next, the calcined product was sufficiently crushed and molded into a disc shape with a diameter of 17 mm using a mold.
Sintered porcelain was obtained by firing in air at 1200-1400°C for 1 hour. The porcelain thus obtained is 2mm thick.
A device was made by polishing a sample and baking electrodes on both sides, and its electrical characteristics were measured. The electrical characteristics are as follows: 1m on the element at 25℃
Operation start voltage V1mA when a current of A flows,
Voltage nonlinear coefficient α at 25℃, V1mA at 25℃
The rate of change △v ₁ /v ₁ between
The ratio of the limiting voltage V ₄₀ A and V 1 mA when a current of 40 A was applied was determined. The nonlinear coefficient α is obtained by approximating the change in the element current I with respect to the voltage V by the following equation. I=(v/c)〓 Here, C is the voltage per 1 mm of the thickness of the element when the current density is 1 mA/cm ² . Table 1 also shows the measurement results of the electrical properties when the blending composition of the porcelain was varied. The blended compositions shown in Table 1 are expressed in atomic % calculated from the ratio of the number of atoms of the added element to the total number of atoms of each component metal element in the blended raw materials.

【table】

[Table] Sample No. 1 shown in Table 1 corresponds to conventional porcelain manufactured by adding only Nd and Co to ZnO.
The temperature change rate Δv ₁ /v ₁ of V1 mA is -7.5%, and the ratio of the limiting voltage to the operation start voltage V ₄₀ /V ₁ mA is 2.2.
The V1 mA temperature stability and limiting voltage characteristics, which are the objects of the present invention, are good. That is, △v ₁ /v ₁
is closer to 0 than -7.5%, and samples with V ₄₀ A/V ₁ mA of 2.2 or less are Nos. 3-8, 11-14, 17-
20, 23-26. Therefore, Nd is 0.1 to 5.0 at%, Co is 0.5 to 5.0 at%, Cs is 0.05 to 0.5 at%,
It can be seen that Cr needs to be added within the range of 0.05 to 0.5 at%. As mentioned above, as is clear from Table 1, by adding Cs and Cr to Nd and Co as subcomponents,
The temperature characteristics and limiting voltage characteristics of V ₁ mA are greatly improved. This is achieved only when Nd, Co, Cs, and Cr coexist in ZnO. If these subcomponents are added alone, voltage nonlinearity will be extremely poor and only nearly ohmic characteristics will be obtained. Furthermore, if only Cs or Cr is added in addition to Nd and Co, the resistance becomes high or low and voltage nonlinearity is lost, making it impossible to put it to practical use as a varistor. As described above, the voltage non-linear resistance ceramic of the present invention maintains good voltage non-linearity and has a V ₁ m
The temperature characteristics and limiting voltage characteristics of A are greatly improved, and therefore it can be used extremely effectively as a varistor.

Claims (1)

[Claims] 1 Zinc oxide is the main component, and neodymium, cobalt, cesium and chromium are added as subcomponents in the form of elements or compounds, each converted to an element,
Neodymium is 0.1-5.0 at%, cobalt is 0.5-5.0
atomic%, cesium is 0.05 to 0.5 atomic%, chromium is
Voltage nonlinear resistance porcelain characterized by being made by adding and firing in a range of 0.05 to 0.5 at%.