Multilayer varistor and manufacturing method thereof

Abstract

To provide a multilayer varistor capable of improving moisture resistance reliability by forming a high resistance layer that contains Zn2SiO4 over the surface of a Pr-containing element.SOLUTION: A multilayer varistor 1 includes: a ceramic body 11; an internal electrode 12 placed inside the ceramic body 11; a high resistance layer 13 placed on the surface of the ceramic body 11; and an external electrode 14 that is placed on a part of the surface of the high resistance layer 13 and connected to the internal electrode 12. The ceramic body 11 includes Zinc oxide and praseodymium oxide, but includes no bismuth oxide. The high resistance layer 13 includes Zn2SiO4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a multilayer varistor and a method for manufacturing a multilayer varistor, and more particularly to a multilayer varistor including a ceramic body and a high-resistance layer, and a method for manufacturing a multilayer varistor. [Background technology]

[0002] Multilayer varistors are used in various electronic devices and other electronic equipment for the purposes of protecting the devices and other electronic equipment from abnormal voltages caused by lightning surges, static electricity, and the like, and also for the purposes of preventing malfunctions of the devices and other electronic equipment caused by noise generated in the circuits.

[0003] In multilayer varistors, a SiO2 layer is formed as a high-resistance layer on the surface of a ceramic body to improve plating resistance and ensure moisture-resistant reliability. Patent Document 1 discloses a conductive chip-type ceramic element that is a multilayer varistor. This ceramic element includes a conductive chip-type ceramic body, terminal electrodes having a baked electrode layer formed by baking a conductive paste containing a metal powder and an inorganic binder, and a plating layer, and an insulating inorganic layer having a melting point or softening point higher than the baking temperature used to form the baked electrode. The insulating inorganic layer is composed of SiO2 or 50 wt. % or more of SiO2, with the remainder being an oxide such as Al2O3. Patent Document 1 describes that such an insulating inorganic layer reacts with and melts with the inorganic binder during the formation of the baked electrode layer, and is absorbed into the baked electrode layer and disappears.

[0004] In conventional multilayer varistors such as those disclosed in Patent Document 1, reactive melting of the insulating inorganic layer causes the insulating inorganic layer to become non-uniform, making it susceptible to insulation degradation due to reaction between the exposed ceramic element and the plating solution. Furthermore, loss of the insulating inorganic layer not only directly under the external electrodes but also at the edges of the external electrodes reduces the sealing performance between the ceramic element and the external electrodes, potentially allowing moisture to penetrate into the multilayer varistor. Due to these factors, conventional multilayer varistors have the disadvantage of being prone to a decrease in moisture resistance reliability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-251210 Summary of the Invention [Problem to be solved by the invention]

[0006] To address this drawback, it is believed that the moisture-resistant reliability of the multilayer varistor can be improved by replacing the SiO2 layer serving as a high-resistance layer with a ceramic crystal layer having a higher resistance and a higher melting point, such as a Zn2SiO4 layer.In the case of a Bi-based varistor whose ceramic body contains ZnO and bismuth (Bi) oxide as its main components, it is known that by performing heat treatment at a temperature of 800°C or higher, the Bi oxide in the ceramic body acts to cause the ZnO in the ceramic body to react with the SiO2 in the high-resistance layer to produce Zn2SiO4, thereby forming a high-resistance layer.

[0007] However, in the case of Pr-based varistors, whose ceramic body contains ZnO and praseodymium (Pr) oxide as its main components, adding Bi oxide to the ceramic body has a significant effect on the conductive mechanism, particularly at the grain boundaries of the ceramic body, and reduces the basic performance of the varistor, so the above-mentioned formation method cannot be used.As a result, it is not possible to form a Zn2SiO4 layer as a high-resistance layer in Pr-based varistors.

[0008] An object of the present disclosure is to provide a multilayer varistor capable of improving moisture resistance reliability by forming a Zn2SiO4-containing high-resistance layer on the surface of a Pr-containing element body, and a method for manufacturing the multilayer varistor. [Means for solving the problem]

[0009] A laminated varistor according to one aspect of the present disclosure includes a ceramic body, an internal electrode provided inside the ceramic body, a high-resistance layer provided on a surface of the ceramic body, and an external electrode provided on a portion of the surface of the high-resistance layer and connected to the internal electrode. The ceramic body contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide. The high-resistance layer contains Zn2SiO4.

[0010] A method for manufacturing a laminated varistor according to one aspect of the present disclosure includes the steps of: preparing a ceramic body having internal electrodes therein; forming a high-resistance layer on a surface of the ceramic body; and forming an external electrode on a portion of the surface of the high-resistance layer so as to connect to the internal electrodes. The ceramic body contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide. The high-resistance layer contains Zn2SiO4. [Effects of the Invention]

[0011] According to the multilayer varistor of the present disclosure, the moisture-resistant reliability can be improved by forming a Zn2SiO4-containing high-resistance layer on the surface of the Pr-containing element body. Also, according to the method for manufacturing a multilayer varistor of the present disclosure, the moisture-resistant reliability can be improved by forming a Zn2SiO4-containing high-resistance layer on the surface of the Pr-containing element body, and thus the multilayer varistor can be manufactured simply and reliably. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a multilayer varistor according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a multilayer varistor according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1. Overview The outline of the multilayer varistor 1 will be explained below with reference to the drawings. Note that the drawings are schematic diagrams, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios.

[0014] The inventors have conducted extensive research and have investigated various methods for forming a high resistance layer in a multilayer varistor, and have found that the above-mentioned problems can be solved, thereby completing the present disclosure.

[0015] The multilayer varistor 1 of this embodiment comprises a ceramic body 11, an internal electrode 12 provided inside the ceramic body 11, a high-resistance layer 13 provided on the surface of the ceramic body 11, and an external electrode 14 provided on part of the surface of the high-resistance layer 13 and connected to the internal electrode 12. The ceramic body 11 contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide. The high-resistance layer 13 contains Zn2SiO4.

[0016] According to the multilayer varistor 1 of this embodiment, the moisture resistance reliability can be improved by forming a Zn2SiO4-containing high-resistance layer on the surface of the Pr-containing element body. "Moisture resistance reliability" means the good moisture resistance of the multilayer varistor evaluated by a pressure cooker bias test (PCBT) (conditions: 121°C, 100% RH, 2 atmospheres, DC applied: 85% of the varistor voltage). The moisture resistance reliability of the multilayer varistor is evaluated by the varistor voltage (V 1mA ) decrease (ΔV 1mA ) is less than 10%, or the varistor voltage (V 1μA ) decrease (ΔV 1μA ) is 50% or less, it can be evaluated as good.

[0017] In the multilayer varistor 1 of this embodiment, when the high-resistance layer 13 is in contact with the ceramic body 11, the ceramic body 11 does not contain Bi oxide, and the high-resistance layer 13 does not contain Bi oxide, thereby eliminating the effects of Bi oxide diffusion and the like. Therefore, the Zn2SiO4-containing high-resistance layer 13 can be formed by a method that does not require the action of Bi oxide for its formation. Furthermore, even when the high-resistance layer 13 of the multilayer varistor 1 contains Bi oxide, the effects of Bi oxide diffusion from the high-resistance layer 13 to the ceramic body 11 can be suppressed by providing an intermediate layer 15 between the ceramic body 11 and the high-resistance layer 13. Therefore, the Zn2SiO4-containing high-resistance layer 13 can be formed by both a method that does not require the action of Bi oxide and a method that does require the action of Bi oxide for its formation. These features enable the multilayer varistor 1 to improve its moisture-resistant reliability.

[0018] 2.Details <Multilayer varistor> The multilayer varistor 1 will be described in detail with reference to FIGS.

[0019] It is sufficient that the multilayer varistor 1 is provided with at least one pair of internal electrodes 12 and at least one pair of external electrodes 14. The multilayer varistor 1 of FIGS. 1 and 2 has four internal electrodes 12 (two pairs) and two external electrodes 14 (one pair). The internal electrodes 12 include, for example, two first internal electrodes 12A and two second internal electrodes 12B. The external electrodes 14 include, for example, a first external electrode 14A provided on one end face of the ceramic body 11 and a second external electrode 14B provided on the other end face of the ceramic body 11. The first internal electrode 12A is connected to the first external electrode 14A, and the second internal electrode 12B is connected to the second external electrode 14B, specifically, electrically. In the multilayer varistor 1, one of the first external electrode 14A and the second external electrode 14B is a high-potential electrode, and the other is a low-potential electrode.

[0020] In this embodiment, "provided on the surface" means being directly or indirectly overlaid on the surface, that is, it includes not only being in contact with the surface, but also being present at a distance from the surface or via another layer.

[0021] [First embodiment] FIG. 1 shows a multilayer varistor 1 according to the first embodiment. The multilayer varistor 1 of the first embodiment comprises a ceramic body 11, internal electrodes 12, a high-resistance layer 13 in contact with the ceramic body 11, and an external electrode 14. The ceramic body 11 contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide. The high-resistance layer 13 contains Zn2SiO4, but does not contain bismuth oxide.

[0022] In the multilayer varistor 1 of the first embodiment, even when the high-resistance layer 13 is in contact with the ceramic body 11, the Zn2SiO4-containing high-resistance layer 13 can be formed, thereby improving the moisture-resistant reliability.

[0023] (ceramic body) The ceramic body 11 is made of, for example, a semiconductor ceramic component having nonlinear resistance characteristics. The ceramic body 11 contains zinc oxide such as ZnO as a main component and PrO as a secondary component. 31 , PrO 11 Ceramic body 11 may contain, as a secondary component, Co2O3, MnO2, Sb2O3, CaCO3, Cr2O3, etc. Ceramic body 11 is formed by the semiconductor ceramic components in which zinc oxide, the main component, is dissolved and sintered with part of the secondary component, praseodymium oxide, etc., and the remaining secondary component precipitates at the grain boundaries.

[0024] (Internal electrode) The internal electrode 12 is provided inside the ceramic body 11. The internal electrode 12 contains a metal component such as Ag, Pd, PdAg, or PtAg. The ceramic body 11 having the internal electrode 12 therein is formed, for example, by stacking ceramic sheets coated with an internal electrode paste containing the above-mentioned metal component, and firing the stack.

[0025] (High resistance layer) The high-resistance layer 13 is in contact with the ceramic body 11. That is, the high-resistance layer 13 directly overlaps the ceramic body 11, and the high-resistance layer 13 is provided on the surface of the ceramic body 11. The high-resistance layer 13 may be provided so as to cover part of the surface of the ceramic body 11, but it is preferable that the high-resistance layer 13 be provided so as to cover the entire surface of the ceramic body 11.

[0026] The high resistance layer 13 contains Zn2SiO4 and does not contain bismuth oxide.

[0027] Such a high-resistance layer 13 containing Zn2SiO4 and not containing Bi oxide can be formed using a method that does not require the action of Bi oxide for its formation, for example, by atomic layer deposition (ALD).

[0028] The average thickness of the high-resistance layer 13 is, for example, 0.01 μm or more and 5.0 μm or less, and preferably 0.1 μm or more and 1.5 μm or less. The "average thickness" refers to the arithmetic mean value of thicknesses measured at multiple points (for example, any 10 points) on the high-resistance layer 13.

[0029] (external electrode) The external electrode 14 is provided on a part of the surface of the high resistance layer 13, that is, provided so as to cover a part of the high resistance layer 13, and is connected to the internal electrode 12, specifically, electrically connected thereto.

[0030] The external electrodes 14 contain metal components such as Ag, AgPd, AgPt, etc., and glass components such as Bi2O3, SiO2, B2O3, etc. The external electrodes 14 preferably contain a metal as their main component, and more preferably contain Ag as their main component.

[0031] The external electrode 14 may have a single layer structure (external electrode 14A and external electrode 14B) or a multilayer structure having multiple layers.

[0032] The external electrodes 14 are usually formed by applying an external electrode paste containing the above-mentioned metal components to a portion of the surface of the high resistance layer 13 and baking it.

[0033] (plating electrode) The plating electrodes are provided on at least a portion of the surface of the external electrode 14, that is, they are provided so as to cover at least a portion of the external electrode 14. The plating electrodes include, for example, Ni electrodes provided so as to cover at least a portion of the external electrode 14, and Sn electrodes provided so as to cover at least a portion of the Ni electrodes.

[0034] [Second embodiment] FIG. 2 shows a multilayer varistor 1 according to the second embodiment. The multilayer varistor 1 of the second embodiment comprises a ceramic body 11, internal electrodes 12, high-resistance layers 13, and external electrodes 14, as well as an intermediate layer 15 between the ceramic body 11 and the high-resistance layer 13. The ceramic body 11 contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide. The high-resistance layer 13 contains Zn2SiO4 and bismuth oxide.

[0035] In the multilayer varistor 1 of the second embodiment, by providing the intermediate layer 15, it is possible to form the Zn2SiO4-containing high-resistance layer 13, thereby improving the moisture resistance reliability.

[0036] The ceramic body 11, internal electrodes 12, external electrodes 14 and plated electrodes in the multilayer varistor 1 of the second embodiment are the same as those in the multilayer varistor 1 of the first embodiment.

[0037] (middle class) The intermediate layer 15 is provided between the ceramic body 11 and the high-resistance layer 13. By providing the intermediate layer 15, it is possible to suppress the effect on the performance of the multilayer varistor 1 of the diffusion of Bi oxide from the high-resistance layer 13 to the ceramic body 11. This makes it possible to form a high-resistance layer containing Zn2SiO4 by both methods requiring the action of Bi oxide and methods not requiring the action of Bi oxide. The intermediate layer 15 may be one layer or two or more layers.

[0038] Examples of layers constituting the intermediate layer 15 include a single-layer structure such as an SiO2 layer or an Al2O3 layer, and a two-layer structure such as an SiO2 layer / Al2O3 layer or an Al2O3 layer / SiO2 layer on the ceramic body 11 side / high-resistivity layer 13 side. Of these, the Al2O3 layer is preferred from the viewpoints of further suppressing the diffusion of Bi oxide from the high-resistivity layer 13 to the ceramic body 11 and promoting the reaction of forming a Zn2SiO4 layer in the high-resistivity layer 13. The SiO2 layer is preferred from the viewpoints of further suppressing the diffusion of Al2O3 to the ceramic body 11 and acting as a bonding aid between the Zn2SiO4-containing high-resistivity layer 13 or the Al2O3 intermediate layer 15 and the ceramic body 11, thereby improving bonding strength. To further exert these effects, the intermediate layer 15 preferably has a two-layer structure of an SiO2 layer / Al2O3 layer on the ceramic body 11 side / high-resistivity layer 13 side. That is, it is more preferable that the multilayer varistor 1 has a layer structure of ceramic body 11 / SiO2 layer / Al2O3 layer / Zn2SiO4 layer.

[0039] The intermediate layer 15 can be formed by any method that does not require the action of Bi oxide for its formation, such as a method in which a precursor slurry containing a precursor material of the intermediate layer 15 is applied, followed by heat treatment to dehydrate and harden it, or a method using atomic layer deposition (ALD).

[0040] The total average thickness of the intermediate layer 15 is, for example, 0.1 μm or more and 10 μm or less, and preferably 0.5 μm or more and 5 μm or less.

[0041] (High resistance layer) The high-resistance layer 13 contains Zn2SiO4 and bismuth oxide. In the multilayer varistor 1 of the second embodiment, an intermediate layer 15 is provided between the ceramic body 11 and the high-resistance layer 13. Therefore, even if the high-resistance layer 13 contains Bi oxide, the influence of diffusion of this Bi oxide into the ceramic body 11 is suppressed, and the high-resistance layer 13 containing Zn2SiO4 can be formed by a method requiring the action of Bi oxide. The high-resistance layer 13 may be one layer or two or more layers, but is usually one layer.

[0042] Examples of methods for forming the Zn2SiO4-containing high-resistance layer 13 include a method of applying a mixture of ZnO, SiO2, and Bi2O3 to the surface of the intermediate layer 15 and then performing a heat treatment, and a method of stacking a ZnO layer, an SiO2 layer, and a Bi2O3 layer by ALD and then performing a heat treatment.

[0043] The average thickness of the high resistance layer 13 is, for example, 0.1 μm or more and 2.0 μm or less, and preferably 0.5 μm or more and 1.5 μm or less.

[0044] <Manufacturing method of multilayer varistor> [First embodiment] The method for manufacturing the multilayer varistor 1 of the first embodiment includes the following first, second, and third steps: In the manufacturing method of the first embodiment, the high-resistance layer 13 contains Zn2SiO4 and does not contain bismuth oxide.

[0045] (1st step) In the first step, a ceramic body 11 having an internal electrode 12 therein, containing zinc oxide and praseodymium oxide, and not containing bismuth oxide, is prepared.

[0046] In the first step, the ceramic element 11 may be produced. For example, an internal electrode paste is applied to ceramic sheets produced using a slurry containing zinc oxide and praseodymium oxide, and the ceramic sheets are laminated, pressed, cut, and then debindered and fired to produce the ceramic element 11 having the internal electrodes 12 therein. The slurry may contain, for example, ZnO as the main raw material and Pr2O3 and Pr6O as auxiliary raw materials. 11 and the like, and a binder.

[0047] As the internal electrode paste, for example, Ag paste, Pd paste, Pt paste, PdAg paste, PtAg paste, etc. can be used.

[0048] The temperature for removing the binder is, for example, 300° C. to 500° C. The firing temperature can be adjusted appropriately depending on the structure, composition, etc. of the ceramic body 11 to be obtained, and is, for example, 800° C. to 1300° C.

[0049] (2nd process) In the second step, a high-resistance layer 13 containing Zn2SiO4 is formed on the surface of the ceramic body 11 prepared in the first step.

[0050] In the second step, the Zn2SiO4-containing high-resistance layer 13 is preferably formed by atomic layer deposition (ALD). By forming the high-resistance layer 13 by atomic layer deposition, the multilayer varistor 1 having improved moisture resistance reliability can be manufactured more simply and reliably.

[0051] ALD is a method for forming layers composed of atomic layer deposition (ALD) by repeatedly introducing a gaseous precursor to the surface on which the layer is to be formed, irradiating it with O2 plasma, Ar plasma, or the like, or oxidizing it with H2O, etc. The Zn2SiO4-containing high-resistivity layer 13 is formed, for example, by first forming a preliminary layer for forming the Zn2SiO4 layer on the surface of the ceramic body 11, consisting of two Zn-containing layers and a Si-containing layer between the Zn-containing layers, followed by O2 plasma irradiation, etc. The Si-containing layer is formed using precursors such as tetra(1-methoxy-2-methyl-2-propoxy)silane (Si(MMP)4), tetraethoxysilane (Si(OEt)4), or tetraisocyanatosilane (Si(NCO)4), followed by purging. The Zn-containing layer is formed using a precursor such as zinc bis(6-ethyl-2,2-dimethyloctane-3,5-dicarboxylate) (Zn(EDMDD)2) or zinc bis(2,4-octanedionato) (Zn(OD)2), followed by purging. This preliminary layer formation is repeated until the desired thickness, such as 0.1 μm to 2.0 μm, is reached, followed by annealing at a temperature of preferably 400°C or higher to form a Zn2SiO4 layer. This preliminary layer formation may be performed by repeating the formation of a Zn-containing layer and a Si-containing layer in a 2:1 ratio.

[0052] According to the method for forming the Zn2SiO4 layer using ALD in this way, the Zn2SiO4 layer is also formed at the interface with the ceramic body 11, so that the ceramic body 11 and the high-resistance layer 13 can be firmly bonded together.

[0053] (3rd step) In the third step, an external electrode paste is applied to a portion of the surface of the high-resistance layer 13 formed in the second step so as to connect to the internal electrode 12, and then baked to form the external electrode 14. The external electrode paste can be prepared by mixing a metal component containing, for example, Ag powder, AgPd powder, or AgPt powder, a glass component containing, for example, Bi2O3, SiO2, or B2O3, and a solvent. Alternatively, an external electrode paste containing Ag as the main component and a resin component can also be used. Examples of methods for applying the external electrode paste include dipping and printing. The baking temperature is, for example, 700°C or higher and 800°C or lower.

[0054] (4th step) The manufacturing method of the multilayer varistor 1 usually includes a fourth step of forming a plated electrode. In the fourth step, the plated electrode is formed on at least a part of the surface of the external electrode 14, that is, the plated electrode is formed so as to cover a part of the external electrode 14. Examples of a method for forming the plated electrode include a method in which Ni plating and Sn plating are performed in this order by electrolytic plating.

[0055] [Second embodiment] The method for manufacturing the multilayer varistor 1 of the second embodiment includes the following first step, second step, a step of forming an intermediate layer after the first step and before the second step, and third step. In the manufacturing method of the second embodiment, the high-resistance layer 13 contains Zn2SiO4 and bismuth oxide.

[0056] (1st step) The first step of the second embodiment is the same as the first step of the first embodiment.

[0057] (Intermediate layer formation process) In the intermediate layer forming step, intermediate layer 15 is formed on the surface of ceramic body 11. This intermediate layer 15 may be a single layer or multiple layers. Furthermore, this intermediate layer 15 may be formed so as to be in contact with ceramic body 11, or may be formed via another layer that is in contact with ceramic body 11.

[0058] In the intermediate layer forming step, the intermediate layer 15 is preferably formed by atomic layer deposition (ALD). By forming the intermediate layer 15 by atomic layer deposition, it is possible to more simply and reliably manufacture the multilayer varistor 1 having improved moisture resistance reliability.

[0059] ALD is performed by using, for example, Si(MMP)4 as a precursor and irradiating O2 plasma to form an SiO2 layer, and by using, for example, trimethylaluminum as a precursor and irradiating O2 plasma to form an Al2O3 layer.

[0060] The intermediate layer 15 can also be formed by, for example, applying a slurry containing precursor materials for each layer to be formed and then performing a heat treatment.

[0061] (2nd process) In the second step, a high resistance layer 13 containing Zn2SiO4 and bismuth oxide is formed on the surface of the intermediate layer 15 formed in the intermediate layer forming step.

[0062] In the second step of the second embodiment, for example, a mixture of ZnO, SiO2 and Bi2O3 is applied, and then heat treatment is performed at a temperature of 800°C or higher, thereby forming a high-resistance layer 13 containing Zn2SiO4 and Bi oxide.

[0063] The high-resistance layer 13 can also be formed by atomic layer deposition (ALD). That is, a ZnO layer, an SiO2 layer, and a Bi2O3 layer are formed by ALD on the surface of the intermediate layer 15 in a stacked manner, and then heat treatment is performed at a temperature of 800°C or higher to form the high-resistance layer 13 containing Zn2SiO4 and Bi oxide. The ZnO layer is formed by ALD using a precursor such as Zn(EDMDD)2 and oxidizing it by irradiating it with O2 plasma or by introducing H2O or O2 gas.

[0064] (3rd process, 4th process) The third and fourth steps of the second embodiment are the same as the third and fourth steps of the first embodiment.

[0065] As described above, by the method for manufacturing the multilayer varistor 1 of this embodiment, it is possible to simply and reliably manufacture a multilayer varistor 1 having improved moisture resistance reliability by forming a Zn2SiO4-containing high-resistance layer on the surface of the Pr-containing element body.

[0066] (summary) As is clear from the above embodiments, the present disclosure includes the following aspects. In the following, reference numerals are given in parentheses only to clarify the correspondence with the embodiments.

[0067] The laminated varistor (1) of the first aspect comprises a ceramic body (11), an internal electrode (12) provided inside the ceramic body (11), a high-resistance layer (13) provided on the surface of the ceramic body (11), and an external electrode (14) provided on part of the surface of the high-resistance layer (13) and connected to the internal electrode (12). The ceramic body (11) contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide. The high-resistance layer (13) contains Zn2SiO4.

[0068] According to the first aspect, the monolithic varistor (1) can improve its moisture-resistant reliability by forming a Zn2SiO4-containing high-resistance layer on the surface of the Pr-containing element body.

[0069] In the laminated varistor (1) of the second embodiment, the high resistance layer (13) of the first embodiment is in contact with the ceramic body (11) and does not contain bismuth oxide.

[0070] According to the second aspect, even when the high-resistance layer (13) is in contact with the ceramic body (11), the Zn2SiO4-containing high-resistance layer (13) can be formed, thereby improving the moisture resistance reliability of the multilayer varistor (1).

[0071] The laminated varistor (1) of the third aspect is the same as that of the first or second aspect, and further comprises an intermediate layer (15) between the ceramic body (11) and the high-resistance layer (13). The high-resistance layer (13) contains bismuth oxide.

[0072] According to the third aspect, by providing the intermediate layer (15), a Zn2SiO4-containing high resistance layer (13) can be formed, and the moisture resistance reliability of the multilayer varistor (1) can be improved.

[0073] A method for manufacturing a laminated varistor (1) according to a fourth aspect includes a first step, a second step, and a third step. In the first step, a ceramic body (11) having internal electrodes (12) therein is prepared. In the second step, a high-resistance layer (13) is formed on the surface of the ceramic body (11). In the third step, an external electrode (14) is formed on a part of the surface of the high-resistance layer (13) so as to connect to the internal electrode (12). The ceramic body (11) contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide. The high-resistance layer (13) contains Zn2SiO4.

[0074] According to the fourth aspect, a multilayer varistor (1) having improved moisture resistance reliability can be produced simply and reliably by forming a Zn2SiO4-containing high-resistance layer on the surface of a Pr-containing element body.

[0075] In a fifth aspect of the method for producing a laminated varistor (1), in the fourth aspect, the high resistance layer (13) does not contain bismuth oxide. In the second step, the high resistance layer (13) is formed by atomic layer deposition.

[0076] According to the fifth aspect, by forming the high resistance layer (13) by atomic layer deposition, it is possible to more simply and reliably manufacture the multilayer varistor (1) having improved moisture resistance reliability.

[0077] The sixth aspect of the method for producing a laminated varistor (1) in the fourth or fifth aspect further comprises a step of forming an intermediate layer (15) by atomic layer deposition after the first step and before the second step. The high resistance layer (13) contains bismuth oxide.

[0078] According to the sixth aspect, by forming the intermediate layer (15) by atomic layer deposition, it is possible to more simply and reliably manufacture the multilayer varistor (1) having improved moisture resistance reliability. [Explanation of symbols]

[0079] 1 Multilayer varistor 11 Ceramic body 12 Internal electrode 13 High resistance layer 14 External electrode 15 Middle Class

Claims

1. A ceramic body; an internal electrode provided inside the ceramic body; a high-resistance layer provided on the surface of the ceramic body; an external electrode provided on a part of the surface of the high resistance layer and connected to the internal electrode; Equipped with the ceramic body contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide; The high resistance layer is made of Zn ２ SiO ４ Contains Multilayer varistor.

2. The high-resistance layer is in contact with the ceramic body and does not contain bismuth oxide. The multilayer varistor according to claim 1 .

3. an intermediate layer is further provided between the ceramic body and the high-resistance layer; The high resistance layer contains bismuth oxide. The multilayer varistor according to claim 1 .

4. A first step of preparing a ceramic body having internal electrodes therein; a second step of forming a high-resistance layer on the surface of the ceramic body; a third step of forming an external electrode on a part of the surface of the high resistance layer so as to connect to the internal electrode; Equipped with the ceramic body contains zinc oxide and praseodymium oxide, but does not contain bismuth oxide; The high resistance layer is made of Zn ２ SiO ４ Contains A method for manufacturing a multilayer varistor.

5. the high-resistance layer does not contain bismuth oxide, In the second step, the high resistance layer is formed by atomic layer deposition. A method for producing the laminated varistor according to claim 4.

6. After the first step and before the second step, Further comprising the step of forming an intermediate layer by atomic layer deposition; The high resistance layer contains bismuth oxide. A method for producing the laminated varistor according to claim 4.

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