Zinc oxide varistor and producing method for the zinc oxide varistor

Abstract

To provide a zinc oxide varistor produced by adding oxide and lithium fluoride to zinc oxide, which is capable of sintering at a low temperature, and provide a producing method for the same.SOLUTION: A zinc oxide varistor 1A includes: a varistor element body 2A formed by using zinc oxide as a main component and a mixed material obtained by adding oxide and lithium fluoride to zinc oxide; and a plurality of electrodes 3A. The varistor element body 2A is a mixed material in which zinc oxide (ZnO) is used as a main component and oxide and lithium fluoride (LiF) are added to zinc oxide. Such a mixed material is prepared, a molded body is formed using the mixed material, and the molded body is fired to form a sintered body, thereby forming a varistor element body 2A. Further, the zinc oxide varistor 1A can be manufactured by forming a plurality of electrodes on the sintered body. The zinc oxide varistor 1A can eliminate or reduce the amount of precious metal such as palladium (Pd).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a zinc oxide varistor and a method for manufacturing a zinc oxide varistor. [Background technology]

[0002] In recent years, the rapid increase in frequency and capacity of electronic devices has led to a rapid spread of various electronic devices, including mobile phones. Voltage limiting elements such as zinc oxide varistors are widely used in such devices to protect against various surges, pulse noise, and ESD, as well as to protect the device's circuits, ensure operational stability, and comply with noise regulations.

[0003] Zinc oxide varistors, which are made by adding bismuth oxide (Bi2O3) to zinc oxide (ZnO), are known to exhibit excellent nonlinearity in their current-voltage characteristics. This material is generally fired at high temperatures of around 1200°C. In particular, in structures with internal electrodes within layers in multilayer chip varistors, a silver-palladium (Ag-Pd) alloy with palladium added is used as the electrode material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-005499 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if sintering at low temperatures becomes possible, there will be no need to use precious metals such as palladium (Pd), or the amount of precious metals used can be reduced.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a zinc oxide varistor that can be sintered at a low temperature and a method for producing a zinc oxide varistor. [Means for solving the problem]

[0007] In one embodiment, a zinc oxide varistor is provided, comprising a varistor element body formed using a mixed material containing zinc oxide as a main component and having an oxide and lithium fluoride added to the zinc oxide, and a plurality of electrodes formed on the varistor element body.

[0008] In one embodiment, the lithium fluoride is added at a ratio of 0.01 to 0.2 mol % relative to the zinc oxide.

[0009] In one embodiment, there is provided a method for manufacturing a zinc oxide varistor, which comprises preparing a mixed material containing zinc oxide as a main component and adding an oxide and lithium fluoride to the zinc oxide, forming a compact using the mixed material, and firing the compact to form a sintered body, thereby obtaining a varistor element.

[0010] In one embodiment, the lithium fluoride is added at a ratio of 0.01 to 0.2 mol % relative to the zinc oxide. In one embodiment, the compact is fired at a temperature of 1000°C. [Effects of the Invention]

[0011] Zinc oxide varistors, which are manufactured by adding oxides and lithium fluoride to zinc oxide, can be sintered at low temperatures. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 illustrates an embodiment of a zinc oxide varistor. [Figure 2] FIG. 10 shows another embodiment of a zinc oxide varistor. [Figure 3] FIG. 1 shows a comparative example of fired pellets and samples 1 to 7. [Figure 4] 1 is a graph showing the dependency of the nonlinearity coefficient α calculated from the current-voltage characteristics on the amount of lithium fluoride (LiF) added. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings described below, identical or corresponding components are designated by the same reference numerals, and duplicated descriptions will be omitted. In the multiple embodiments described below, the configuration of an embodiment that is not particularly described is the same as that of other embodiments, and therefore duplicated descriptions will be omitted.

[0014] Fig. 1 is a diagram showing one embodiment of a zinc oxide varistor. Fig. 2 is a diagram showing another embodiment of a zinc oxide varistor. In the embodiment shown in Fig. 1, zinc oxide varistor 1A is a disk-type zinc oxide varistor. In the embodiment shown in Fig. 2, zinc oxide varistor 1B is a multilayer chip-type zinc oxide varistor.

[0015] In the embodiment shown in Figure 1, the zinc oxide varistor 1A comprises an annular varistor element body 2A, a circular electrode 3A formed on the varistor element body 2A, and a lead wire 4 connected to the electrode 3A.

[0016] 2, the zinc oxide varistor 1B comprises a varistor element body 2B and an internal electrode 3Ba stacked on top of each other, and an external electrode 3Bb covering the varistor element body 2B and the internal electrode 3Ba. The varistor element body 2B and the internal electrode 3Ba have a plate shape and are arranged alternately in the vertical direction.

[0017] Hereinafter, in this specification, zinc oxide varistors 1A and 1B may be referred to without any particular distinction as zinc oxide varistor 1. Similarly, varistor elements 2A and 2B may be referred to without any particular distinction as varistor element 2.

[0018] The varistor element body 2 is a mixed material whose main component is zinc oxide (ZnO), to which oxides and lithium fluoride (LiF) are added. Such a mixed material is prepared, a compact is formed using the mixed material, and the compact is fired to form a sintered body, which becomes the varistor element body 2. Furthermore, by forming multiple electrodes on the sintered body, it is possible to manufacture a zinc oxide varistor 1. The zinc oxide varistor 1 can eliminate or reduce the amount of precious metals such as palladium (Pd) used.

[0019] Furthermore, a sheet material is created from the above-mentioned mixed material, and a paste containing silver (Ag) is printed on this sheet material. The sheet material that will become the varistor element body 2 and internal electrode 3Ba is constructed, and multiple sheets of this sheet material are prepared and stacked, then cut to a specified size to form a compact. This compact is fired to form a sintered body. An external electrode 3Bb is formed on the end face of this sintered body. The zinc oxide varistor 1 formed in this way allows the internal electrodes and varistor element body to be fired simultaneously at a lower temperature than conventional methods.

[0020] In the manufacturing process of zinc oxide varistor 1, Li is introduced into the interstitial sites of zinc oxide (ZnO). + The inclusion of these elements is thought to have the effect of increasing the carrier density. Therefore, samples were prepared by adding oxides and lithium fluoride (LiF) to zinc oxide, and an evaluation was carried out as a varistor element 2 based on the sinterability of the zinc oxide varistor and the nonlinearity in the current-voltage characteristics. The evaluation method and results are explained below.

[0021] The evaluation method was as follows. Zinc oxide (ZnO), bismuth oxide (Bi2O3), antimony oxide (Sb2O3), and lithium fluoride (LiF) were used as raw material powders. The raw material powders were weighed out in a molar ratio of Zn:Bi:Sb:Li = 100:1:2:x (x = 0 to 0.4), and trace amounts of other additives were added to the raw material powders. These raw material powders were wet-mixed in 2-propanol for 2 hours using a mortar and pestle, and the mixed powder was dried.

[0022] The mixed powder was dried and then calcined in air at 600°C for 5 hours. After calcination, it was crushed for 1 hour. A pressure of 40 MPa was applied to the crushed powder, and pellets with a diameter of 10 mm were produced by uniaxial pressing.

[0023] The pellets were subjected to main firing in air for two hours at temperatures of 900°C, 1000°C, and 1100°C. Note that these firing temperatures include not only the actual temperatures but also temperatures controlled or set to such temperatures. Of these, the pellets fired at 1000°C for two hours were selected as the comparative example and samples 1 to 7, respectively. The amounts of lithium fluoride (LiF) added to the comparative example and samples 1 to 7 are shown in Table 1.

[0024] [Table 1]

[0025] Fig. 3 shows the comparative example of sintered pellets and Samples 1 to 7. As shown in Fig. 3, the microstructure of the comparative example and Samples 1 to 7 obtained was observed using a scanning electron microscope (SEM), and the crystalline phase was identified using X-ray diffraction (XRD). In addition, an In-Ga alloy was applied to both sides of the sample as electrodes, and the current-voltage characteristics were measured.

[0026] The evaluation results are as follows. As is clear from Table 1 and Figure 3, grain growth is promoted as the amount of lithium fluoride (LiF) added increases. Furthermore, voids were observed between the zinc oxide (ZnO) particles in the sample to which lithium fluoride (LiF) was added.

[0027] 4 is a graph showing the dependence of the nonlinearity coefficient α calculated from the current-voltage characteristics on the amount of lithium fluoride (LiF) added. As the amount of lithium fluoride (LiF) added increases, the nonlinearity coefficient α increases, reaching a maximum value at 0.03 mol%.

[0028] However, when lithium fluoride (LiF) is added in an amount of 0.03 mol% or more, the nonlinearity coefficient α decreases. It is thought that a small amount of Li ions enters the interstitial sites of zinc oxide (ZnO) and acts as donors to increase the carrier density, which increases the nonlinearity coefficient α.

[0029] On the other hand, when the amount of added Li ions exceeds a certain value, Li ions substitute for the Zn site, and the Li ions at the Zn site act as acceptors, reducing the carrier density. This is thought to be why the nonlinearity coefficient α decreases.

[0030] Varistor characteristics were obtained for each of Samples 1 to 7. In particular, Samples 1 to 5 (containing lithium fluoride added at a ratio of 0.01 to 0.2 mol % to zinc oxide) are more suitable for use as varistor elements.

[0031] According to this embodiment, sintering can be performed at a lower temperature than conventional methods, improving the efficiency of zinc oxide varistor production. Therefore, the manufacturing method of this embodiment contributes to reducing energy consumption and CO2 emissions in the production process and can reduce the use of precious metals.

[0032] Therefore, the zinc oxide varistor 1 manufactured by the manufacturing method according to this embodiment can contribute to the achievement of Goal 3 "Good health and well-being," Goal 7 "Affordable and clean energy," and Goal 12 "Responsible consumption and production" in the Sustainable Development Goals (SDGs) led by the United Nations.

[0033] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0034] 1A,1B Zinc Oxide Varistor 2A, 2B varistor element 3A electrode 3Ba internal electrode 3Bb external electrode 4 lead wires

Claims

1. A zinc oxide varistor, a varistor element formed using a mixed material containing zinc oxide as a main component and adding oxides and lithium fluoride to the zinc oxide; a plurality of electrodes formed on the varistor element body.

2. 2. The zinc oxide varistor according to claim 1, wherein the lithium fluoride is added at a ratio of 0.01 to 0.2 mol % relative to the zinc oxide.

3. A method for manufacturing a zinc oxide varistor, comprising the steps of: preparing a mixed material containing zinc oxide as a main component and adding oxides and lithium fluoride to the zinc oxide; forming a compact using the mixed material; A method for producing a zinc oxide varistor, in which the green body is fired to form a sintered body as a varistor element.

4. 4. The method for producing a zinc oxide varistor according to claim 3, wherein the lithium fluoride is added at a ratio of 0.01 to 0.2 mol % relative to the zinc oxide.

5. 5. The method for producing a zinc oxide varistor according to claim 3, wherein the molded body is fired at a temperature of 1000°C.

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