Varistor and manufacturing method thereof

Abstract

To provide a varistor which is excellent in moisture-proof performance.SOLUTION: A varistor (1) includes a sintered body (11), an internal electrode (12), an insulating layer (13), and an external electrode (14). The internal electrode (12) is arranged inside the sintered body (11). The insulating layer (13) covers at least a part of the sintered body (11), and contains Zn2SiO4. The external electrode (14) is electrically connected to the internal electrode (12), covers a part of the sintered body (11) and a part of the insulating layer (13), and is brought into contact with a part of the insulating layer (13). Average thickness in a region contacting the external electrode (14) of the insulating layer (13) is larger than average thickness in a region not contacting the external electrode (14) of the insulating layer (13).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a varistor and a method for manufacturing a varistor, and more particularly to a varistor including a sintered body, an internal electrode, an insulating layer, and an external electrode, and a method for manufacturing a varistor. [Background technology]

[0002] Varistors are used to protect various electronic equipment and devices from abnormal voltages caused by lightning surges, static electricity, etc., and to prevent malfunctions of electronic equipment and devices caused by noise generated in circuits.

[0003] Varistors are required to have durability that prevents performance degradation even after long-term use. In particular, under high humidity conditions, moisture penetrates the interior and generates conductive carriers, which increases leakage current over time, worsening the power consumption of electronic devices and decreasing the voltage nonlinearity of the varistor. Therefore, there is a demand for improved moisture resistance in varistors.

[0004] Patent Document 1 discloses a varistor comprising a varistor element whose main component is ZnO, a pair of external electrodes formed on part of the surface of the varistor element, and a high-resistivity Zn-Si-O or Bi-Si-O compound layer formed on the entire surface except for the areas where the external electrodes are formed.

[0005] Patent Document 2 describes a varistor comprising a sintered body formed by sintering a laminate in which varistor layers and internal electrodes are alternately stacked, and a pair of external electrodes provided in a state in which the internal electrodes are alternately connected on at least both end faces of the sintered body, in which a glass layer is formed near the second external electrode of the sintered body. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-035706 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-270328 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in recent years, as varistors are used in harsher environments such as in-vehicle devices, the demand for moisture resistance has increased even further, and the conventional varistors described above are unable to meet this demand.

[0008] An object of the present disclosure is to provide a varistor with excellent moisture resistance and a method for manufacturing a varistor. [Means for solving the problem]

[0009] A varistor according to one aspect of the present disclosure comprises a sintered body, an internal electrode, an insulating layer, and an external electrode. The internal electrode is disposed inside the sintered body. The insulating layer covers at least a portion of the sintered body and contains Zn2SiO4. The external electrode is electrically connected to the internal electrode, covers a portion of the sintered body and a portion of the insulating layer, and is in contact with a portion of the insulating layer. The average thickness of the insulating layer in the region in contact with the external electrode is greater than the average thickness of the insulating layer in the region not in contact with the external electrode.

[0010] A method for manufacturing a varistor according to one embodiment of the present disclosure comprises a first step, a second step, a third step, and a fourth step. In the first step, a sintered body containing ZnO as a main component and having internal electrodes disposed therein is prepared. In the second step, a precursor layer containing SiO2 or silicate is formed so as to cover at least a portion of the sintered body. In the third step, an external electrode paste containing Bi2O3 is applied so as to cover a portion of the sintered body and to contact a portion of the precursor layer. In the fourth step, a heat treatment is performed to form an insulating layer containing Zn2SiO4 from the precursor layer, and external electrodes are formed from the external electrode paste. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a varistor with excellent moisture resistance and a method for manufacturing a varistor. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of a varistor according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1. Overview The varistor 1 according to this embodiment comprises a sintered body 11, an internal electrode 12, an insulating layer 13, and an external electrode 14. As shown in Fig. 1, the varistor 1 has a feature that the average thickness of the insulating layer 13 in the region in contact with the external electrode 14 (hereinafter also referred to as the contact region thickness) is greater than the average thickness of the insulating layer 13 in the region not in contact with the external electrode 14 (hereinafter also referred to as the non-contact region thickness).

[0014] The inventors, through careful investigation of each configuration of the varistor, discovered that when the composition of the components contained in the external electrode is varied, the thickness of the insulating layer formed in the region in contact with the external electrode can be varied, and that increasing this thickness improves the moisture resistance of the varistor, and thus completed the present disclosure.

[0015] Thus, the varistor 1 has excellent moisture resistance. The reason why moisture resistance improves when the contact region thickness of the insulating layer 13 is made larger than the non-contact region thickness is not entirely clear, but it can be inferred as follows, for example. That is, it is thought that moisture under high humidity conditions passes through the continuous tiny pores present in the insulating layer 13, passes through the end faces of the sintered body 11, and reaches the sintered body 11 between the internal electrodes 12. In conventional varistors, the contact region thickness and non-contact region thickness of the insulating layer 13 are approximately the same, but in the varistor 1 of this embodiment, the contact region thickness is larger, and therefore there are fewer continuous tiny pores, making it possible to reduce moisture penetration compared to conventional varistors, and as a result, it is thought that moisture resistance can be improved.

[0016] The manufacturing method of the varistor 1 according to this embodiment comprises steps 1, 2, 3, and 4. In step 1, a sintered body 11 containing ZnO as a main component and having internal electrodes disposed therein is prepared. In step 2, a precursor layer containing SiO or silicate is formed so as to cover at least a portion of the sintered body 11. In step 3, an external electrode paste containing BiO is applied so as to cover a portion of the sintered body 11 and to come into contact with a portion of the precursor layer. In step 4, a heat treatment is performed to form an insulating layer 13 containing ZnSiO from the precursor layer, and an external electrode 14 is formed from the external electrode paste.

[0017] In the manufacture of the varistor 1, the insulating layer 13 is formed by a reaction between the ceramic components and the glass components in the sintered body 11. According to the manufacturing method of this embodiment, the insulating layer 13 containing Zn2SiO4 is formed by a reaction between the ZnO contained in the sintered body 11 and the SiO2 or silicate contained in the precursor layer, and it is believed that the Bi2O3 contained in the external electrode paste has a significant effect of promoting this formation reaction. As a result, the thickness of the contact region of the insulating layer 13 can be made larger than the thickness of the non-contact region, making it easy to manufacture a varistor with excellent moisture resistance.

[0018] 2.Details <Barista> The varistor 1 in Fig. 1 comprises a sintered body 11, an internal electrode 12, an insulating layer 13, and an external electrode 14. Each component will be described below.

[0019] [Sintered body] The sintered body 11 is the part that exhibits the voltage nonlinearity of the varistor 1, and is usually made of a semiconductor ceramic component. The sintered body 11 is usually made of a laminated body made up of multiple layers.

[0020] The sintered body 11 contains, for example, ZnO, SrTiO3, SiC, etc. as main components, and Bi2O3, Co3O4, MnO2, Sb2O3, Pr6O as secondary components. 11 , CaCO3, Cr2O3, etc. The sintered body 11 preferably contains ZnO. In this case, the ZnO in the sintered body 11 can react with SiO2, etc. to produce Zn2SiO4, which makes it easy to form the insulating layer 13.

[0021] It is preferable that the sintered body 11 contains substantially no Bi2O3, or that the Bi2O3 concentration in the sintered body 11 is lower than the Bi2O3 concentration in the external electrodes 14. Bi2O3 is thought to have a significant effect of promoting the formation of the insulating layer 13 through a reaction between the semiconductor ceramic component contained in the sintered body 11 and a glass component such as SiO2, and by setting the Bi2O3 concentration in the sintered body 11 in this way, the thickness of the contact region of the insulating layer 13 can be made greater than the thickness of the non-contact region, resulting in further improvement in the moisture resistance of the varistor 1. "Concentration" refers to the ratio (mass %) of the mass of that component to the total mass.

[0022] [Internal electrode] The internal electrodes 12 are disposed inside the sintered body 11. In Fig. 1, the number of internal electrodes 12 is two, but this is not limited thereto and may be three or more, and a desired electrode structure can be formed.

[0023] The internal electrodes 12 are formed using an internal electrode paste containing, for example, Ag, Pd, Pt, PdAg, PtAg, or the like.

[0024] [Insulating layer] The insulating layer 13 covers at least a part of the sintered body 11. In the varistor 1 of Fig. 1, the insulating layer 13 covers the entire surface of the sintered body 11 except for the end faces.

[0025] The insulating layer 13 contains Zn2SiO4. When the insulating layer 13 contains Zn2SiO4, the linear expansion coefficients of the insulating layer 13 and the sintered body 11 become closer, improving the crack resistance of the varistor 1 and thereby improving the moisture resistance. In addition to Zn2SiO4, the insulating layer 13 may contain, for example, Bi4(SiO2)4, SiO2, etc.

[0026] The insulating layer 13 containing Zn2SiO4 can be formed by applying a coating liquid containing a glass component such as SiO2 or silicate to cover at least a part of the sintered body 11 to form a precursor layer, and then heat-treating the precursor layer, resulting in a reaction between the semiconductor ceramic component such as ZnO contained in the sintered body 11 and the glass component such as SiO2 contained in the precursor layer.

[0027] The average thickness of the insulating layer 13 in the region in contact with the external electrode 14 is greater than the average thickness in the region not in contact with the external electrode 14. The "average thickness" refers to the arithmetic mean value of the thickness of the insulating layer 13 measured at any 10 points in each of the contact region and non-contact region. However, if the average thickness in the region not in contact with the external electrode 14 is zero, it is not possible to specify the magnitude relationship between the thickness of the contact region and the thickness of the non-contact region.

[0028] The thickness of the non-contact region is, for example, 0.01 μm or more and 10 μm or less, preferably 0.1 μm or more and 7 μm or less, and more preferably 1 μm or more and 5 μm or less. The thickness of the contact region is, for example, 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 40 μm or less, and more preferably 5 μm or more and 30 μm or less. The value obtained by subtracting the non-contact region thickness from the contact region thickness is, for example, 1 μm to 20 μm, preferably 3 μm to 15 μm, and more preferably 5 μm to 10 μm. The ratio of the contact area thickness to the non-contact area thickness (contact area thickness / non-contact area thickness) is, for example, 1.1 or more and 10 or less, preferably 2 or more and 8 or less, and more preferably 3 or more and 5 or less. By setting the contact region thickness in this way, the moisture resistance of the varistor 1 can be further improved.

[0029] [External electrode] The external electrode 14 is electrically connected to the internal electrode 12, covers part of the sintered body 11 and part of the insulating layer 13, and is in contact with part of the insulating layer 13. In the varistor 1 of Fig. 1, the external electrode 14 covers the end of the sintered body 11 and is in contact with the insulating layer 13 at the contact region.

[0030] The external electrodes 14 contain, for example, metals such as Ag, and glass components such as Bi2O3, SiO2, and B2O5. The external electrodes 14 preferably contain Bi2O3. Bi2O3 is thought to have a significant effect of promoting the formation of the insulating layer 13 through a reaction between the semiconductor ceramic component contained in the sintered body 11 and the glass component. Therefore, when the external electrodes 14 contain Bi2O3, the reaction for forming the insulating layer 13 is further promoted in the region in contact with the external electrodes 14, the thickness of the contact region increases, and the moisture resistance of the varistor 1 can be further improved.

[0031] 1, the varistor 1 may have, as an external electrode, a primary external electrode 15 in addition to the external electrode 14 (secondary external electrode). The primary external electrode 15 is disposed on the sintered body 11 side, and is in contact with a part (first region) of the insulating layer 13. The secondary external electrode 14 covers the primary external electrode 15, and is in contact with a second region of the insulating layer 13 that is different from the first region.

[0032] In this way, when the varistor 1 comprises the primary external electrode 15 and the secondary external electrode 14 as external electrodes, it is preferable that the average thickness of the second region (region in contact with the secondary external electrode 14) of the insulating layer 13 is greater than the average thickness of the first region (region in contact with the primary external electrode 15) of the insulating layer 13. In this case, the average thickness of the insulating layer 13 in the region in contact with the secondary external electrode 14 becomes greater, and the moisture resistance of the varistor 1 can be further improved.

[0033] Furthermore, when the varistor 1 comprises a primary external electrode 15 and a secondary external electrode 14 as external electrodes, it is preferable that the primary external electrode 15 is substantially free of Bi2O3, or that the Bi2O3 concentration in the primary external electrode 15 is lower than the Bi2O3 concentration in the secondary external electrode 14. Bi2O3 is thought to have a significant effect of promoting the formation of the insulating layer 13 through a reaction between the semiconductor ceramic component contained in the sintered body 11 and a glass component such as SiO2, and by setting the Bi2O3 concentration in the primary external electrode 15 in this way, the contact region thickness of the insulating layer 13 (average thickness of the region in contact with the secondary external electrode 14) can be made larger, and as a result, the moisture resistance of the varistor 1 can be further improved.

[0034] <Varistor manufacturing method> The method for manufacturing a varistor according to this embodiment comprises steps 1, 2, 3, and 4. The method for manufacturing a varistor according to this embodiment is a method for manufacturing a varistor 1 of this embodiment in which the main component of the sintered body 11 is ZnO, the insulating layer 13 is formed from a precursor layer containing SiO2 or silicate, and the external electrode 14 contains Bi2O3. Each step will be explained below.

[0035] [1st step] In this step, a sintered body 11 containing ZnO as a main component and having an internal electrode 12 disposed therein is prepared.

[0036] The sintered body 11 can be produced by printing an internal electrode paste on a sheet made using, for example, a slurry containing ZnO, stacking the sheets, pressing, cutting, removing the binder, firing, and chamfering.

[0037] The slurry can be prepared by mixing, for example, ZnO as a main raw material, Bi2O3, Co3O4, MnO2, etc. as auxiliary raw materials, and a binder.

[0038] The internal electrode paste may be, for example, Ag paste, Pd paste, Pt paste, PdAg paste, PtAg paste, or the like.

[0039] The temperature at which the binder is removed is, for example, 300° C. or higher and 500° C. or lower. The temperature at which the firing is carried out can be appropriately adjusted depending on the constituent composition of the resulting sintered body 11, and is, for example, 800° C. or higher and 1300° C. or lower. Chamfering is usually carried out after firing, but may be carried out before firing.

[0040] Preferably, the sintered body 11 is substantially free of Bi2O3, or the Bi2O3 concentration in the sintered body 11 is lower than the Bi2O3 concentration in the external electrode paste. Bi2O3 is thought to have a significant effect of promoting the formation of the insulating layer 13 containing Zn2SiO4 through a reaction between the semiconductor ceramic component contained in the sintered body 11 and the SiO2 or silicate contained in the precursor layer, and by setting the Bi2O3 concentration in the sintered body 11 in this way, the thickness of the contact region of the insulating layer 13 can be made greater than the thickness of the non-contact region, resulting in further improved moisture resistance of the varistor.

[0041] [Second process] In this step, a precursor layer containing SiO2 or silicate is formed so as to cover at least a part of the sintered body 11 prepared in the first step.

[0042] The precursor layer can be formed by applying a coating liquid containing, for example, SiO 2 or a silicate such as sodium silicate to at least a part of the sintered body 11, followed by dehydration and curing.

[0043] The application method is not particularly limited, and any one of dipping, spraying, vacuum impregnation, printing, etc., or a combination of these may be used.

[0044] The temperature for dehydration and curing is, for example, 220° C. or higher and 250° C. or lower, and the time is, for example, 0.1 hours or higher and 2 hours or lower.

[0045] When forming a primary external electrode 15 as an external electrode in addition to the secondary external electrode 14, it is preferable to apply a primary external electrode paste before the second step or the third step to only the end surfaces of the sintered body 11 so as to cover part of the sintered body 11, come into contact with part of the precursor layer, and not extend beyond the main planes of the sintered body 11. The primary external electrode paste can be prepared by mixing a metal such as Ag powder, glass frit containing Bi2O3, SiO2, BO5, etc., a vehicle, and a solvent. It is preferable that the primary external electrode paste does not contain glass frit. After applying the primary external electrode paste, it is preferable to perform baking under conditions of, for example, 600°C to 800°C for 10 minutes to 1 hour.

[0046] [3rd step] In this step, an external electrode paste (secondary external electrode paste) containing Bi2O3 is applied so as to cover a portion of the sintered body 11 and to come into contact with a portion of the precursor layer formed in step 2. When the primary external electrode 15 is formed, the secondary external electrode paste is applied in a predetermined shape so as to cover the primary external electrode 15.

[0047] The secondary external electrode paste can be prepared by mixing, for example, Ag powder metal, glass frit containing Bi2O3, BO5, Co3O4, SiO2, etc., a vehicle, and a solvent. The secondary external electrode paste preferably does not contain SiO2, in order to suppress precipitation on the surface of the external electrode after firing. The Bi2O3 content in the secondary external electrode paste is preferably 3% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less. In this case, the thickness of the insulating layer 13 in the region in contact with the secondary external electrode 14 can be increased, thereby further improving the moisture resistance of the varistor.

[0048] [4th step] In this step, by performing heat treatment, an insulating layer containing Zn2SiO4 is formed from the precursor layer, and an external electrode (secondary external electrode 14) is formed from the external electrode paste (secondary external electrode paste).

[0049] The heat treatment conditions are, for example, 800° C. or higher and 900° C. or lower, and 5 minutes or higher and 1 hour or lower.

[0050] This heat treatment forms an external electrode (secondary external electrode 14) from the external electrode paste (secondary external electrode paste), and the SiO2 or silicate contained in the precursor layer reacts with the ZnO contained in the sintered body 11 to form an insulating layer 13 containing Zn2SiO4. In this case, due to the action of Bi2O3 contained in the external electrode paste (secondary external electrode paste), the thickness of the insulating layer 13 in the region in contact with the external electrode 14 becomes greater than the thickness of the region not in contact with the external electrode 14.

[0051] The method for manufacturing a varistor according to this embodiment may further include, after the first to fourth steps, a step of performing Ni plating, Sn plating, or the like by electrolytic plating, for example.

[0052] The varistor manufactured in the above manner has a larger average thickness in the region of insulating layer 13 that is in contact with external electrode 14 than in the region of insulating layer 13 that is not in contact with external electrode 14, and this varistor has superior moisture resistance. [Example]

[0053] Hereinafter, the present disclosure will be described more specifically with reference to examples, but the present disclosure is not limited to only these examples.

[0054] <Varistor manufacturing> The varistor of Example 1 was manufactured by the following procedure. [Preparation of sintered body] (Preparation of slurry) The main raw material, ZnO, the secondary raw materials, Bi2O3, Co3O4, MnO2, etc., and a binder were mixed to prepare a slurry.

[0055] (Sheet production) The prepared slurry was molded into a sheet having a predetermined thickness of 20 μm or more and 50 μm or less.

[0056] (Preparation of laminate) The internal electrode paste was made of Ag paste, and the internal electrode paste was printed in a predetermined shape on the prepared sheet, and laminated to obtain a predetermined electrode structure. This was pressed to a predetermined thickness, and then cut to a predetermined shape (in this example, dimensions of 1.6 mm in length, 0.8 mm in width, and 0.8 mm in height) to prepare a laminate.

[0057] (Production of sintered body) The produced laminate was subjected to binder removal at 300° C. to 500° C., then fired at 800° C. to 1300° C., and then chamfered to produce a sintered body.

[0058] [Formation of primary external electrodes] The primary external electrode paste was prepared by mixing Ag powder, glass frit containing Bi2O3, SiO2 and B2O5, a vehicle and a solvent. This primary external electrode paste was applied to the main flat surfaces of the sintered body, only onto the edge faces so as not to spill over, and then baked at 800°C for 1 hour to form the primary external electrodes.

[0059] [Preparation of coated body] A sodium silicate aqueous solution was used as a coating liquid for forming a precursor layer. The coating liquid was applied to the sintered body prepared above, and then dehydration and curing were carried out at 220°C or higher and 250°C or lower for 1 hour to form a precursor layer, thereby producing a coated body.

[0060] [Formation of secondary external electrode] The secondary external electrode paste was prepared by mixing Ag powder, glass frit containing Bi2O3, BO5, and Co3O4, a vehicle, and a solvent. This secondary external electrode was applied in a predetermined shape to the prepared coating body so as to cover the primary external electrode.

[0061] After applying the secondary external electrode paste, baking was performed at 800°C or higher and 900°C or lower for 10 minutes to form an insulating layer 13 containing Zn2SiO4 from the precursor layer, and a secondary external electrode 14 was formed from the secondary external electrode paste.

[0062] [Preparation of plated body] A Ni plating of a predetermined thickness was formed by electrolytic plating, and then an Sn plating was formed thereon to obtain the varistor of Example 1.

[0063] In Comparative Example 1, a varistor was produced in the same manner as in Example 1, except that no insulating layer was formed. In Comparative Example 2, a varistor was manufactured in the same manner as in Example 1, except that an external electrode paste not containing Bi2O3 was used.

[0064] <Evaluation> [Humidity load test] The varistors thus produced were subjected to a humidity load test under the conditions shown below to evaluate their moisture resistance. (Conditions) Temperature: 85°C, Relative humidity: 85%RH, Load voltage: Varistor voltage V1mA x 85%, Test time: 2000 hours (Sample form) A plated product was used. However, in Comparative Example 1, a product after external electrodes were formed was used because of plating runaway. (Moisture resistance evaluation characteristics) Leakage current characteristics: The rate of change (%) of the varistor voltage V1μA when a current of 1μA is applied before and after the humidity load test. This indicates the characteristics in the region where the varistor does not switch. The larger the rate of change, the larger the leakage current will be during actual use. Voltage nonlinearity: This is the voltage ratio (V1mA / V10μA) of the varistor voltage V1mA when a current of 1mA is passed through it and the varistor voltage V10μA when a current of 10μA is passed through it after a humidity load test. This is a general characteristic of varistors and is a value that indicates nonlinearity. A large value indicates poor voltage nonlinearity.

[0065] [Table 1]

[0066] The results in Table 1 show that the varistor of Example 1 has an insulating layer and the contact region thickness is greater than the non-contact region thickness, and is therefore excellent in moisture resistance in terms of leakage current characteristics and voltage nonlinearity. On the other hand, the varistor of Comparative Example 1 has an insulating layer that does not contain Zn2SiO4, and the varistor of Comparative Example 2 has the same contact region thickness and non-contact region thickness, and is therefore inferior in moisture resistance.

[0067] As is clear from the above-described embodiments and examples, the varistor (1) according to the first aspect of the present disclosure comprises a sintered body (11), an internal electrode (12), an insulating layer (13), and an external electrode (14). The internal electrode (12) is disposed inside the sintered body (11). The insulating layer (13) covers at least a portion of the sintered body (11) and contains Zn2SiO4. The external electrode (14) is electrically connected to the internal electrode (12), covers a portion of the sintered body (11) and a portion of the insulating layer (13), and is in contact with a portion of the insulating layer (13). The average thickness of the insulating layer (13) in the region in contact with the external electrode (14) is greater than the average thickness of the insulating layer (13) in the region not in contact with the external electrode (14).

[0068] According to the first aspect, by making the thickness of the contact area greater than the thickness of the non-contact area, it is believed that the penetration of moisture into the sintered body (11) under high humidity conditions, which occurs through the insulating layer (13) from the contact area where the adhesion between the insulating layer (13) and the external electrode (14) is weak, can be reduced compared to conventional varistors, and as a result, the varistor (1) can be made to have excellent moisture resistance. Furthermore, according to the first aspect, the linear expansion coefficients of the insulating layer (13) and the sintered body (11) become closer, improving the crack resistance of the varistor (1), and thereby further improving the moisture resistance.

[0069] In the second aspect of the present disclosure, the sintered body (11) in the first aspect contains ZnO.

[0070] According to the second embodiment, ZnO contained in the sintered body (11) can react with SiO2 or the like to produce Zn2SiO4, and the insulating layer (13) can be easily formed.

[0071] In a third aspect of the present disclosure, in the first or second aspect, the external electrode (14) contains Bi2O3.

[0072] According to the third aspect, the external electrode (14) contains Bi2O3, which is believed to have a significant effect of promoting the formation of an insulating layer (13) due to a reaction between the semiconductor ceramic component contained in the sintered body (11) and the glass component. This further promotes the formation of the insulating layer (13) in the region in contact with the external electrode (14), increases the thickness of the contact region, and further improves the moisture resistance of the varistor (1).

[0073] In a fourth aspect of the present disclosure, the sintered body (11) in the third aspect is substantially free of Bi2O3, or the Bi2O3 content concentration in the sintered body (11) is lower than the Bi2O3 content concentration in the external electrode (14).

[0074] According to the fourth aspect, by setting the concentration of BiO in the sintered body (11) as described above, which is believed to have a significant effect of promoting the formation of the insulating layer (13) due to the reaction between the semiconductor ceramic component contained in the sintered body (11) and the glass component such as SiO, the thickness of the contact region of the insulating layer (13) can be made larger than the thickness of the non-contact region, and as a result, the moisture resistance of the varistor (1) can be further improved.

[0075] In a fifth aspect of the present disclosure, in any one of the first to fourth aspects, the external electrode includes a primary external electrode (15) arranged on the sintered body (11) side and in contact with a first region of the insulating layer (13), and a secondary external electrode (14) covering the primary external electrode (15) and in contact with a second region of the insulating layer (13) different from the first region. The average thickness of the insulating layer (13) in the second region is greater than the average thickness of the insulating layer (13) in the first region.

[0076] According to the fifth aspect, the average thickness of the insulating layer (13) in the region in contact with the secondary external electrode (14) is increased, and the moisture resistance of the varistor (1) can be further improved.

[0077] In a sixth aspect of the present disclosure, in the fifth aspect, the primary external electrode (15) is substantially free of Bi2O3, or the concentration of Bi2O3 in the primary external electrode (15) is lower than the concentration of Bi2O3 in the secondary external electrode (14).

[0078] According to the sixth aspect, by setting the concentration of BiO in the primary external electrode (15) as described above, which is believed to have a significant effect of promoting the formation of the insulating layer (13) due to the reaction between the semiconductor ceramic component contained in the sintered body (11) and the glass component such as SiO, the thickness of the contact area of the insulating layer (13) (the area in contact with the secondary external electrode (14)) can be made larger, and as a result, the moisture resistance of the varistor (1) can be further improved.

[0079] A method for manufacturing a varistor according to a seventh aspect of the present disclosure includes a first step, a second step, a third step, and a fourth step. In the first step, a sintered body (11) containing ZnO as a main component and having an internal electrode (12) disposed therein is prepared. In the second step, a precursor layer containing SiO2 or silicate is formed so as to cover at least a portion of the sintered body (11). In the third step, an external electrode paste containing Bi2O3 is applied so as to cover a portion of the sintered body (11) and to contact a portion of the precursor layer. In the fourth step, a heat treatment is performed to form an insulating layer (13) containing Zn2SiO4 from the precursor layer, and an external electrode (14) is formed from the external electrode paste.

[0080] According to the seventh aspect, an insulating layer (13) containing Zn2SiO4 is formed by a reaction between ZnO contained in the sintered body (11) and SiO2 or silicate contained in the precursor layer, and Bi2O3 contained in the external electrode paste is thought to have a significant effect of promoting this formation reaction, so that the thickness of the contact region of the insulating layer (13) can be made larger than the thickness of the non-contact region, and a varistor with excellent moisture resistance can be easily manufactured.

[0081] In an eighth aspect of the present disclosure, in the seventh aspect, the average thickness of the insulating layer (13) in the region in contact with the external electrode (14) is greater than the average thickness of the insulating layer (13) in the region not in contact with the external electrode (14).

[0082] According to the eighth aspect, the varistor can have better moisture resistance.

[0083] In a ninth aspect of the present disclosure, in the seventh or eighth aspect, the sintered body (11) is substantially free of Bi2O3, or the Bi2O3 content concentration in the sintered body (11) is lower than the Bi2O3 content concentration in the external electrode paste.

[0084] According to the ninth aspect, by setting the content concentration of BiO in the sintered body (11) as described above, which is believed to have a significant effect of promoting the formation of the insulating layer (13) containing ZnSiO due to the reaction between the semiconductor ceramic component contained in the sintered body (11) and the SiO or silicate contained in the precursor layer, the thickness of the contact region of the insulating layer (13) can be made larger than the thickness of the non-contact region, and as a result, the moisture resistance of the varistor can be further improved.

[0085] According to a tenth aspect of the present disclosure, in any one of the seventh to ninth aspects, the content concentration of Bi2O3 in the external electrode paste is 3% by mass or more and 30% by mass or less.

[0086] According to the tenth aspect, the thickness of the insulating layer (13) in the region in contact with the secondary external electrode (14) can be made larger, thereby further improving the moisture resistance of the varistor. [Explanation of symbols]

[0087] 1. Barista 11 Sintered body 12 Internal electrode 13 Insulating layer 14 External electrode (secondary external electrode) 15 Primary external electrode

Claims

1. a sintered body; an internal electrode disposed inside the sintered body; covering at least a portion of the sintered body, ２ SiO ４ an insulating layer comprising an external electrode electrically connected to the internal electrode, covering a part of the sintered body and a part of the insulating layer, and contacting a part of the insulating layer, the external electrode containing Bi 2 O 3 ; Equipped with the average thickness of the insulating layer in the region in contact with the external electrode is greater than the average thickness of the insulating layer in the region not in contact with the external electrode; Barista.

2. The sintered body contains ZnO.

2. The varistor according to claim 1.

3. The sintered body is Bi ２ O ３ or the sintered body is substantially free of Bi. ２ O ３ The concentration of Bi in the external electrodes ２ O ３ The concentration of 3. The varistor according to claim 1 or 2.

4. The external electrode is a primary external electrode disposed on the sintered body side and in contact with a first region of the insulating layer; a secondary external electrode that covers the primary external electrode and is in contact with a second region of the insulating layer that is different from the first region; Including, the average thickness of the insulating layer in the second region is greater than the average thickness of the insulating layer in the first region; A varistor according to any one of claims 1 to 3.

5. The primary external electrode is Bi ２ O ３ or substantially free of Bi in the primary external electrode ２ O ３ The concentration of Bi in the secondary external electrode ２ O ３ The concentration of 5. The varistor according to claim 4.

6. A first step of preparing a sintered body containing ZnO as a main component and having internal electrodes disposed therein; SiO ２ a second step of forming a precursor layer comprising a silicate; Bi to cover a portion of the sintered body and to be in contact with a portion of the precursor layer. ２ O ３ a third step of applying an external electrode paste containing By heat treatment, Zn is removed from the precursor layer. ２ SiO ４ and a fourth step of forming an insulating layer containing the external electrode paste and forming external electrodes from the external electrode paste. Equipped with The sintered body is substantially free of Bi 2 O 3 or the Bi 2 O 3 content in the sintered body is The concentration of Bi 2 O 3 contained therein is lower than the concentration of Bi 2 O 3 contained in the external electrode paste. How to manufacture a varistor.

7. the average thickness of the insulating layer in the region in contact with the external electrode is greater than the average thickness of the insulating layer in the region not in contact with the external electrode; A method for producing the varistor according to claim 6.

8. Bi in the external electrode paste ２ O ３ The content concentration is 3% by mass or more and 30% by mass or less, A method for producing a varistor according to claim 6 or 7.

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