Zinc oxide varistor and method for manufacturing zinc oxide varistor

Abstract

The present application relates to a zinc oxide varistor and a method for manufacturing a zinc oxide varistor. The zinc oxide varistor includes a varistor body formed of a mixed material obtained by adding an oxide and lithium fluoride to zinc oxide as a main component, and a plurality of electrodes.

Description

Technical Field

[0001] This invention relates to zinc oxide varistors and methods for manufacturing zinc oxide varistors. Background Technology

[0002] In recent years, with the rapid increase in the frequency and capacity of electronic devices, various electronic devices, led by mobile phones, have become widespread. In order to cope with various surges, impulse noise, ESD countermeasures, circuit protection, operational stability, and noise limits, voltage limiting components such as zinc oxide varistors are widely used in such devices.

[0003] Zinc oxide varistors with added bismuth oxide (Bi₂O₃) or similar components are known to exhibit excellent nonlinearity in current-voltage characteristics. This material is typically sintered at a high temperature of around 1200°C. In particular, in the structure of a multilayer chip varistor with internal electrodes within its layers, a silver-palladium (Ag-Pd) alloy with added palladium is used as the electrode material.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-005499 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, if sintering can be performed at low temperatures, there is no need to use precious metals such as palladium (Pd), or the amount of precious metals used can be reduced.

[0009] Therefore, the object of the present invention is to provide a zinc oxide varistor that can be sintered at low temperature and a method for manufacturing a zinc oxide varistor.

[0010] Methods for solving problems

[0011] In one embodiment, a zinc oxide varistor is provided. The zinc oxide varistor comprises: a varistor blank formed using a mixed material consisting primarily of zinc oxide and to which oxides and lithium fluoride are added; and a plurality of electrodes formed on the varistor blank.

[0012] In one embodiment, the lithium fluoride is added at a ratio of 0.01 to 0.2 mol% relative to the zinc oxide.

[0013] In one embodiment, a method for manufacturing a zinc oxide varistor is provided. The method involves preparing a mixed material consisting primarily of zinc oxide, with added oxides and lithium fluoride, forming a molded body using the mixed material, and then firing the molded body to form a sintered body, thereby producing a varistor blank.

[0014] In one embodiment, the lithium fluoride is added at a ratio of 0.01 to 0.2 mol% relative to the zinc oxide.

[0015] In one method, the molded body is fired at a temperature of 1000°C.

[0016] Invention Effects

[0017] Zinc oxide varistors, which are manufactured by adding oxides and lithium fluoride to zinc oxide, can be sintered at low temperatures. Attached Figure Description

[0018] Figure 1 This is a diagram illustrating one embodiment of a zinc oxide varistor.

[0019] Figure 2 This is a diagram illustrating another embodiment of a zinc oxide varistor.

[0020] Figure 3 The diagram shows a comparative example of calcined particles and samples 1 to 7.

[0021] Figure 4 This is a graph showing the dependence of the nonlinear coefficient α, calculated from the current-voltage characteristics, on the amount of lithium fluoride (LiF) added. Detailed Implementation

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that in the drawings described below, the same or equivalent constituent elements are labeled with the same reference numerals, and repeated descriptions are omitted. In the various embodiments described below, unless otherwise specified, the configuration of one embodiment is the same as the other embodiments, and therefore repeated descriptions thereon are omitted.

[0023] Figure 1 This is a diagram illustrating one embodiment of a zinc oxide varistor. Figure 2 This is a diagram illustrating another embodiment of a zinc oxide varistor. Figure 1 In the embodiment shown, the zinc oxide varistor 1A is a disk-shaped zinc oxide varistor. Figure 2 In the embodiment shown, the zinc oxide varistor 1B is a multilayer zinc oxide varistor.

[0024] exist Figure 1In the embodiment shown, the zinc oxide varistor 1A includes an annular varistor blank 2A, a circular electrode 3A formed on the varistor blank 2A, and a lead wire 4 connected to the electrode 3A.

[0025] exist Figure 2 In the illustrated embodiment, the zinc oxide varistor 1B comprises a varistor blank 2B and an internal electrode 3Ba stacked on top of each other, and an external electrode 3Bb covering the varistor blank 2B and the internal electrode 3Ba. The varistor blank 2B and the internal electrode 3Ba are plate-shaped and are alternately arranged along the vertical direction.

[0026] In this specification, zinc oxide varistors 1A and 1B will sometimes be referred to as zinc oxide varistors 1 without particular distinction. Similarly, varistor blanks 2A and 2B will sometimes be referred to as varistor blanks 2 without particular distinction.

[0027] The varistor blank 2 is a mixed material obtained by adding oxides and lithium fluoride (LiF) to zinc oxide as the main component. This mixed material is prepared, formed into a molded body, and then sintered to form a sintered body, thus producing the varistor blank 2. Furthermore, by forming multiple electrodes on the sintered body, a zinc oxide varistor 1 can be manufactured. The zinc oxide varistor 1 can eliminate or reduce the amount of precious metals such as palladium (Pd) used.

[0028] Furthermore, a sheet is prepared using the aforementioned mixed material, and a paste containing silver (Ag) is printed onto this sheet. Multiple sheets constituting the varistor blank 2 and internal electrode 3Ba are prepared, stacked, and cut to predetermined sizes to form a molded body. This molded body is then 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 for the simultaneous firing of the internal electrode and the varistor blank at a lower temperature than previously possible.

[0029] In the manufacturing process of zinc oxide varistor 1, it is believed that due to Li + By entering the interstitial sites of zinc oxide (ZnO), the carrier density is increased. Therefore, samples were prepared by adding oxides and lithium fluoride (LiF) to zinc oxide. Evaluation was conducted as a varistor blank 2 based on the sinterability of the zinc oxide varistor and the nonlinearity in its current-voltage characteristics. The evaluation method and results are described below.

[0030] The evaluation method is 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 at a molar ratio of Zn:Bi:Sb:Li = 100:1:2:x (x = 0–0.4), and trace amounts of additives were added to the raw material powders. These raw material powders were wet-mixed in 2-propanol using a mortar and pestle for 2 hours, and the mixed powder was then dried.

[0031] After drying the mixed powder, it was pre-fired in air at 600°C for 5 hours. After pre-firing, it was pulverized for 1 hour. The pulverized powder was then subjected to a pressure of 40 MPa and uniaxial compression molding to produce particles with a diameter of 10 mm.

[0032] The particles were formally calcined in air for 2 hours at temperatures of 900°C, 1000°C, and 1100°C. It should be noted that these calcination temperatures include not only the actual temperature but also the temperature controlled or set. The particles calcined at 1000°C for 2 hours were designated as Comparative Examples and Samples 1 to 7, respectively. The amount of lithium fluoride (LiF) added to the Comparative Examples and Samples 1 to 7 is shown in Table 1.

[0033] [Table 1]

[0034]

[0035] Figure 3 This is a comparative example showing the sintered particles, and diagrams of samples 1 to 7. (See diagram for reference.) Figure 3 As shown, the microstructure of the obtained comparative examples and samples 1 to 7 was observed using a scanning electron microscope (SEM), and the crystal phase was identified using X-ray diffraction (XRD). Additionally, In-Ga alloy was coated on both sides of the samples as electrodes, and the current-voltage characteristics were measured.

[0036] The evaluation results are as follows. (From Table 1 and...) Figure 3 This indicates that grain growth is promoted with increasing lithium fluoride (LiF) content. Furthermore, voids were observed between zinc oxide (ZnO) particles in the samples containing lithium fluoride (LiF).

[0037] Figure 4 This is a graph showing the dependence of the nonlinear coefficient α, calculated from the current-voltage characteristics, on the amount of lithium fluoride (LiF) added. The nonlinear coefficient α increases with increasing lithium fluoride (LiF) content, reaching its maximum at 0.03 mol%.

[0038] However, if more than 0.03 mol% of lithium fluoride (LiF) is added, the nonlinear coefficient α decreases. This is because trace amounts of Li ions enter the interstitial sites of zinc oxide (ZnO) lattice, acting as donors and increasing the carrier density, thus increasing the nonlinear coefficient α.

[0039] On the other hand, when the amount of Li ions added exceeds a certain value, Li ions begin to replace Zn sites, and the Li ions at the Zn sites act as acceptors, reducing the carrier density. Therefore, the nonlinear coefficient α is considered to decrease.

[0040] Varistor characteristics were obtained in each of the samples 1 to 7. In particular, samples 1 to 5 (containing added lithium fluoride at a ratio of 0.01 to 0.2 mol% relative to zinc oxide) were more suitable as varistor blanks.

[0041] According to this embodiment, sintering can be performed at a lower temperature than conventional methods, thereby improving the manufacturing efficiency of zinc oxide varistors. Therefore, the manufacturing method of this embodiment helps to reduce energy consumption in the production process, reduce CO2, and reduce the use of precious metals.

[0042] Therefore, the zinc oxide varistor 1 manufactured using the manufacturing method described in this embodiment can contribute to the United Nations-led Sustainable Development Goals (SDGs) Goal 3 "Good Health and Well-being", Goal 7 "Affordable Clean Energy", and Goal 12 "Responsible Consumption and Production".

[0043] The above embodiments are described to enable those skilled in the art to implement the present invention. Various modifications to the above embodiments are readily apparent to those skilled in the art, and the technical concept of the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but should be interpreted as encompassing the widest scope of the technical concept as defined by the claims.

[0044] Industrial availability

[0045] This invention can be used for zinc oxide varistors and methods for manufacturing zinc oxide varistors.

[0046] Explanation of reference numerals in the attached figures

[0047] 1A, 1B Zinc oxide varistors

[0048] 2A, 2B Varistor Blanks

[0049] 3A electrode

[0050] 3Ba internal electrode

[0051] 3Bb external electrode

[0052] 4 Lead wires

Claims

1. Zinc oxide varistor, which has the following characteristics: A varistor blank is formed using a mixed material consisting primarily of zinc oxide, with the addition of oxides and lithium fluoride to the zinc oxide; and Multiple electrodes formed on the varistor blank.

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, wherein, A mixed material is prepared, with zinc oxide as the main component and oxides and lithium fluoride added to the zinc oxide. The mixed material is used to form a molded body. The molded body is sintered to form a sintered body, which is then used to make a varistor blank.

4. The method for manufacturing the 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. The method for manufacturing a zinc oxide varistor according to claim 3 or 4, wherein, The molded body is fired at a temperature of 1000°C.

Images