JP5338795B2 - Chip varistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chip varistor that appropriately maintains ESD withstand, while reducing the capacitance without providing an internal electrode. <P>SOLUTION: An element assembly 3 comprises a varistor part 7; and a support part 9 arranged so as to sandwich the varistor part 7 in a direction orthogonal to an opposite direction of a pair of end faces. The varistor part 7 consists of a sintered body containing ZnO as a main component, extends between the pair of the end faces so as to connect to a terminal electrode, and manifests voltage nonlinear characteristics. The support part 9 consists of a sintered body containing ZnO as a main component, and extends between the pair of the end faces so as to connect to the terminal electrode. The varistor part 7 comprise a first region 8a where at least one kind of an element selected from a group consisting of alkaline metal, An and Cu, exists; and a second region 8b which extends between the pair of the end faces, and where an element selected from the group consisting of alkaline metal, Ag and Cu, does not exist. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a chip varistor.

  As a chip varistor, a varistor element having a varistor layer and an internal electrode arranged so as to sandwich the varistor layer, a terminal electrode arranged to be connected to an internal electrode corresponding to an end of the varistor element, There is known a multilayer chip varistor provided with (for example, see Patent Document 1). In the multilayer chip varistor, a region sandwiched between internal electrodes in the varistor layer functions as a region that develops a voltage nonlinear characteristic (hereinafter also referred to as “varistor characteristic”).

JP 2002-246207 A

  In recent high-speed interfaces, the structure of the IC itself is becoming vulnerable to ESD (Electrostatic Discharge) in order to achieve high speed. For this reason, the request | requirement of the ESD countermeasure in high-speed transmission type | system | group IC is increasing, and the multilayer chip | tip ballus described in patent document 1 is used as an ESD countermeasure component. As a characteristic required for ESD countermeasure parts for high-speed transmission systems, it is essential to reduce electrostatic capacity. If the developed electrostatic capacity is large, there is a problem in signal quality, and in the worst case, communication may be disabled.

  As a method of reducing the capacitance of the multilayer chip varistor, a method of reducing the area of the portion where the internal electrodes overlap with each other can be considered. By reducing the area of the portion where the internal electrodes overlap each other, the area where the electrostatic capacity is generated is reduced, and the electrostatic capacity is reduced. However, if the area of the portion where the internal electrodes overlap with each other (hereinafter referred to as “overlap area”) is reduced, a new problem arises that the resistance to ESD (hereinafter referred to as “ESD resistance”) decreases. When a surge voltage such as ESD is applied, the electric field distribution in the portion where the internal electrodes overlap with each other is concentrated at the end of the portion where the internal electrodes overlap each other. When the electric field distribution of the portion where the internal electrodes overlap each other is concentrated on the end portion, the ESD tolerance decreases rapidly as the overlapping area decreases.

  As described above, since the multilayer chip varistor includes the internal electrode, it is difficult to reduce the capacitance while maintaining good ESD tolerance.

  An object of the present invention is to provide a chip varistor capable of reducing the capacitance while maintaining good ESD resistance without providing an internal electrode.

  The present invention is a chip varistor including an element body including a pair of end faces facing each other and terminal electrodes respectively disposed on the end face side of the element body, and the element body is a sintered body mainly composed of ZnO. A varistor portion that extends over a pair of end faces so as to be connected to the terminal electrode, and that develops a voltage nonlinear characteristic, and a sintered body mainly composed of ZnO, and is connected to the terminal electrode. And a support portion located between the pair of end surfaces and sandwiching the varistor portion in a direction orthogonal to the opposing direction of the pair of end surfaces, the varistor portion being made of a group consisting of alkali metal, Ag, and Cu. A first region containing at least one element selected, and a second region extending between a pair of end faces and free from an element selected from the group consisting of alkali metal, Ag, and Cu. And features.

  In the chip varistor according to the present invention, the varistor portion extends between the pair of end faces so as to be connected to the terminal electrode, and the varistor portion functions as a region that directly expresses the varistor characteristics between the terminal electrodes. That is, the chip varistor of the present invention, unlike the multilayer chip varistor described above, exhibits varistor characteristics between the terminal electrodes without providing an internal electrode. For this reason, even when a surge voltage such as ESD is applied, a portion where the electric field distribution is concentrated does not occur in the varistor part, and the ESD tolerance does not decrease.

In this invention, the varistor part which consists of a sintered compact which has ZnO as a main component contains the 1st area | region where at least 1 type of element chosen from the group which consists of an alkali metal, Ag, and Cu exists. In the varistor part, the first region where at least one element selected from the group consisting of alkali metal, Ag and Cu is present is the second region where no element selected from the group consisting of alkali metal, Ag and Cu is present. Compared to the region, the electric conductivity is low and the relative dielectric constant is low. Therefore, when the varistor portion includes the first region, the capacitance of the varistor portion is reduced, and the capacitance of the chip varistor can be reduced.
In the present invention, the support portion is positioned so as to sandwich the varistor portion in a direction orthogonal to the opposing direction of the pair of end surfaces. Thereby, a varistor part can be reliably protected by a support part.

  The first region of the varistor portion may be located on the outer surface side of the varistor portion so as to sandwich both sides of the second region of the varistor portion when viewed from the opposing direction of the pair of end faces. In this case, since the electric conductivity on the outer surface side of the varistor part is low, the surface current hardly flows on the outer surface of the varistor part. As a result, the occurrence of leakage current can be suppressed.

  The element selected from the group consisting of alkali metal, Ag, and Cu may be present in the first region by diffusing from both side surfaces extending in the opposing direction of the pair of end faces in the varistor part. In this case, since at least one element selected from the group consisting of alkali metals, Ag, and Cu is diffused from the outer surface of the element body, at least one element selected from the group consisting of alkali metals, Ag, and Cu is used. The range in which these elements diffuse can be easily controlled.

  The support part may include a region where at least one element selected from the group consisting of alkali metal, Ag, and Cu is present. In this case, the electrostatic capacity of the support portion is reduced. The capacitance of the chip varistor can be represented by the sum of the capacitances of the varistor part and the support part that are located between the terminal electrodes. Therefore, the capacitance of the chip varistor can be further reduced.

  The support part may contain Sr, Zr, and Co as subcomponents. Zr acts as a substance that suppresses grain growth of ZnO. For this reason, in the support portion, grain growth of ZnO is suppressed, and the crystal grains of ZnO are relatively small. The electric resistance value of the ZnO crystal grain boundary is much larger than that of the ZnO crystal grain, and the electric field is mainly applied to the ZnO crystal grain boundary. For this reason, the electrostatic capacity developed in the sintered body made of ZnO crystal grains is affected by the number of ZnO crystal grain boundaries between the terminal electrodes. That is, when the number of ZnO crystal grain boundaries between the terminal electrodes is small, the capacitance is high, and when the number of ZnO crystal grain boundaries between the terminal electrodes is large, the capacitance is low. Since the ZnO grain growth in the support portion is suppressed and the ZnO crystal grains are relatively small, the number of ZnO crystal grain boundaries between the terminal electrodes is relatively large. For this reason, the electrostatic capacitance of a support part becomes low, and the electrostatic capacitance of a chip varistor can be further reduced.

  Since Sr forms a liquid phase during firing, it functions as a glue that connects the main surface of the varistor part and the main surface of the support part. Therefore, the connection strength at the interface between the varistor part and the support part becomes strong, and the occurrence of peeling between the varistor part and the support part can be suppressed.

  The varistor part may further contain Sr as a subcomponent. In this case, the connection strength at the interface between the varistor part and the support part is further strengthened, and the occurrence of peeling between the varistor part and the support part can be further suppressed.

  According to the present invention, it is possible to provide a chip varistor capable of reducing the capacitance while maintaining good ESD resistance without providing an internal electrode.

It is a perspective view which shows the chip varistor concerning this embodiment. It is a figure explaining the section composition of the chip varistor concerning this embodiment. It is a figure explaining the section composition of the chip varistor concerning this embodiment. It is a figure explaining the section composition of the chip varistor concerning this embodiment. It is a figure for demonstrating the manufacturing process of the chip varistor which concerns on this embodiment. It is a figure for demonstrating the manufacturing process of the chip varistor which concerns on this embodiment. It is a schematic diagram for demonstrating the structure of the element body of the chip varistor which concerns on this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  First, the configuration of the chip varistor 1 according to the present embodiment will be described with reference to FIGS. FIG. 1 is a perspective view showing a chip varistor according to the present embodiment. 2-4 is a figure explaining the cross-sectional structure of the chip varistor based on this embodiment.

  As shown in FIG. 1, the chip varistor 1 includes a substantially rectangular parallelepiped element body 3 and a pair of terminal electrodes 5 formed at both ends of the element body 3. The chip varistor 1 is a chip varistor of a very small size (so-called 0402 size) having a length in the Y direction of 0.4 mm, a height in the Z direction of 0.2 mm, and a width in the X direction of 0.2 mm, for example. .

  The element body 3 includes a varistor portion 7 and a plurality of (two in the present embodiment) support portions 9. The element body 3 has, as outer surfaces, square end faces 3a and 3b facing each other and four side faces 3c to 3f extending in a direction perpendicular to the end faces 3a and 3b. As shown in FIGS. 2 and 3, the support portion 9 sandwiches the varistor portion 7 in a direction intersecting (orthogonal to) the facing direction of the side surfaces 3e and 3f, that is, the facing direction of the end surfaces 3a and 3b.

  The varistor part 7 is a rectangular parallelepiped-shaped part located in the approximate center of the thickness direction (Z direction in the figure) of the element body 3, and is made of a sintered body (semiconductor ceramic) that exhibits varistor characteristics. The varistor portion 7 extends between the end faces 3 a and 3 b of the element body 3. The varistor portion 7 includes a pair of main surfaces 7a and 7b facing in the thickness direction (Y direction in the figure). The thickness of the varistor part 7 is set to about 5 to 100 μm, for example. The main surfaces 7 a and 7 b extend between the end surfaces 3 a and 3 b of the element body 3.

  The varistor part 7 contains ZnO (zinc oxide) as a main component, and Co, rare earth metal elements, group IIIb elements (B, Al, Ga, In), Si, Cr, Mo, alkali metal elements (K) as subcomponents. , Rb, Cs) and alkaline earth metal elements (Mg, Ca, Sr, Ba) and the like, and oxides thereof. In this embodiment, the varistor part 7 contains Co, Pr, Cr, Ca, K, and Al as subcomponents. The ZnO content in the varistor part 7 is not particularly limited, but is usually 99.8 to 69.0% by mass when the total material constituting the varistor part 7 is 100% by mass.

  The rare earth metal element (for example, Pr) acts as a substance that exhibits varistor characteristics. The content of the rare earth metal element in the varistor part 7 is set to about 0.01 to 10 atomic%, for example. Co acts as a substance that assists the expression of varistor characteristics by rare earth metal elements. The Co content in the varistor part 7 is set to, for example, about 0.05 to 50 atomic%. Preferably, the Co content in the varistor part 7 is set to about 0.5 to 10 atomic%, for example.

  The varistor portion 7 further includes side surfaces 7c and 7d extending in the longitudinal direction of the element body 3, and end surfaces 7e and 7f extending in a direction orthogonal to the main surfaces 7a and 7b and the side surfaces 7c and 7d. The side surface 7c constitutes a part of the side surface 3e, and the side surface 7d constitutes a part of the side surface 3f. The end face 7e constitutes a part of the end face 3a, and the end face 7f constitutes a part of the end face 3b.

  As shown in FIGS. 1 and 2, the support portion 9 is a substantially rectangular parallelepiped portion, and is disposed so as to sandwich the varistor portion 7 therebetween. The support portion 9 extends between the end faces 3 a and 3 b of the element body 3. The support portion 9 has a main surface 9a connected to the varistor portion 7 (main surfaces 7a, 7b), and a main surface 9b facing the main surface 9a. The main surfaces 9 a and 9 b extend between the end surfaces 3 a and 3 b of the element body 3. In the present embodiment, substantially the entire main surfaces 7 a and 7 b of the varistor portion 7 are in contact with and connected to the main surface 9 a of the support portion 9. The main surface 9 a of the support portion 9 has substantially the same shape as the main surfaces 7 a and 7 b of the varistor portion 7. The main surface 9 b of the support portion 9 constitutes side surfaces 3 c and 3 d of the element body 3.

  The support part 9 is made of a sintered body containing ZnO as a main component. The support part 9 contains Sr, Zr, and Co as subcomponents. Although content of ZnO in the support part 9 is not specifically limited, When the whole material which comprises the support part 9 is 100 mass%, it is 100-69.0 mass%, for example. The Sr content in the support portion 9 is set to about 0.1 to 30 atomic%, for example. The Zr content in the support portion 9 is set to, for example, about 0.1 to 20 atomic%. The Co content in the support portion 9 is set to, for example, about 0.05 to 50 atomic%. The support portion 9 may contain Ca, Ba, Al, Ga, or the like as a subcomponent in addition to the above Sr, Zr, and Co.

  The support portion 9 further includes side surfaces 9c and 9d extending in the longitudinal direction of the element body 3, and end surfaces 9e and 9f extending in a direction orthogonal to the main surfaces 9a and 9b and the side surfaces 9c and 9d. The side surface 9c constitutes a part of the side surface 3e, and the side surface 9d constitutes a part of the side surface 3f. The end face 9e constitutes a part of the end face 3a, and the end face 9f constitutes a part of the end face 3b.

  The terminal electrode 5 is formed in multiple layers so as to cover the end faces 3 a and 3 b of the element body 3. Therefore, the terminal electrode 5 is connected to the varistor part 7 and the support part 9. The terminal electrode 5 has, for example, a layer structure composed of first to third electrode layers. The first electrode layer includes a conductive powder and glass frit that are directly connected to the varistor portion 7 and the support portion 9 of the element body 3 and are mainly composed of Ag or the like. The second electrode layer is formed so as to cover the first electrode layer and contains Ni as a main component. The third electrode layer is formed so as to cover the second electrode layer and contains Sn as a main component.

  The varistor part 7 and the support part 9 include first regions 8a and 10a and second regions 8b and 10b, respectively, as shown in FIGS. The first regions 8a and 10a contain at least one element selected from the group consisting of alkali metals, Ag, and Cu. In the first regions 8a and 10a, at least one element selected from the group consisting of alkali metal, Ag, and Cu is present as a solid solution in the crystal grains of ZnO, or in the crystal grain boundaries of ZnO. Existing. In the second regions 8b and 10b, an element selected from the group consisting of alkali metals, Ag, and Cu does not exist. In the present embodiment, an alkali metal element, particularly Li, is used as the element. Li has a relatively small ionic radius, is easily dissolved in crystal grains of ZnO, and has a high diffusion rate. In the first regions 8a and 10a, two or more elements selected from the group consisting of alkali metals, Ag, and Cu may exist.

  In the varistor part 7, the second region 8 b is located substantially at the center of the varistor part 7 when viewed from the opposing direction of the end faces 3 a and 3 b (end faces 7 e and 7 f). The second region 8b extends between the end surface 7e and the end surface 7f when viewed from the direction orthogonal to the opposing direction of the end surfaces 3a, 3b (end surfaces 7e, 7f). That is, the second region 8 b extends between the end faces 3 a and 3 b of the element body 3 and is connected to the terminal electrode 5. The first region 8a is located on the outer surface side of the varistor portion 7 so as to sandwich both sides of the second region 8b when viewed from the facing direction of the end surfaces 3a, 3b (end surfaces 7e, 7f). The first region 8a is also connected to the terminal electrode 5 at the end portions in the opposing direction of the end surfaces 3a and 3b (end surfaces 7e and 7f).

  In the support portion 9, the second region 10 b is located on the substantially central side of the element body 3 when viewed from the opposing direction of the end surfaces 3 a and 3 b (end surfaces 9 e and 9 f). The second region 10b extends between the end surface 9e and the end surface 9f when viewed from the direction orthogonal to the opposing direction of the end surfaces 3a, 3b (end surfaces 9e, 9f). That is, the second region 10 b extends between the end faces 3 a and 3 b of the element body 3 and is connected to the terminal electrode 5. The first region 10a is located on the outer surface side of the support portion 9 so as to surround the outside of the second region 8b when viewed from the facing direction of the end surfaces 3a, 3b (end surfaces 7e, 7f). The first region 10a is also connected to the terminal electrode 5 at the end portions in the opposing direction of the end surfaces 3a and 3b (end surfaces 7e and 7f).

  When an element selected from the group consisting of an alkali metal, Ag, and Cu is dissolved in the crystal grains of ZnO, ZnO that exhibits properties as an n-type semiconductor has its donors reduced by the above elements, The electrical conductivity is lowered, and the varistor characteristics are hardly exhibited. It is also considered that the electrical conductivity is lowered by the presence of the above-mentioned elements at the grain boundaries of ZnO. Therefore, the first regions 8a and 10a have lower electrical conductivity and lower capacitance than the second regions 8b and 10b. In the varistor part 7, the second region 8b mainly functions as a region that develops varistor characteristics.

  Subsequently, an example of a manufacturing process of the chip varistor 1 having the above-described configuration will be described with reference to FIGS. 5 and 6 are diagrams for explaining a manufacturing process of the chip varistor according to the present embodiment.

  First, after weighing ZnO which is a main component constituting the varistor part 7 and trace additives such as Co, Pr, Cr, Ca, K, and Al metals or oxides so as to have a predetermined ratio, respectively. The varistor material is prepared by mixing each component. Then, an organic binder, an organic solvent, an organic plasticizer, etc. are added to this varistor material, and it mixes and grind | pulverizes using a ball mill etc., and obtains a slurry. This slurry is applied onto a film made of, for example, polyethylene terephthalate by a known method such as a doctor blade method, and then dried to form a film having a predetermined thickness (for example, about 30 μm). The film thus obtained is peeled from the film to obtain a first green sheet.

  In addition, ZnO, which is a main component constituting the support portion 9, and trace additives such as Sr, Zr, and Co metals or oxides are weighed so as to have a predetermined ratio, and then each component is mixed. Thus, the material for the support portion 9 is adjusted. Then, an organic binder, an organic solvent, an organic plasticizer, etc. are added to the material for this support part 9, and it mixes and grind | pulverizes using a ball mill etc., A slurry is obtained. This slurry is applied onto a film made of, for example, polyethylene terephthalate by a known method such as a doctor blade method, and then dried to form a film having a predetermined thickness (for example, about 30 μm). The film thus obtained is peeled from the film to obtain a second green sheet.

  Next, a predetermined number of first green sheets and second green sheets are stacked, and a varistor green layer made of the first green sheet and a supporting green layer made of the second green sheet are Laminate so as to be sandwiched between supporting green layers. Thereafter, pressure is applied to the stacked green sheets to press the green sheets together. The thickness of the varistor green layer is adjusted by the number of first green sheets. The thickness of the support green layer is adjusted by the number of second green sheets. The number of first green sheets may be at least one.

  As described above, as shown in FIG. 5, a laminate LB in which the varistor green layer L1 and the support green layer L2 are laminated is prepared.

  Next, after drying the stacked body LB, as shown in FIG. 6, the stacked body LB is cut into units of chips to obtain a plurality of green bodies GC (element body 3 before firing). The laminated body LB is cut by, for example, a dicing saw.

  Next, the plurality of green element bodies GC are subjected to heat treatment under predetermined conditions (for example, 180 to 400 ° C. and 0.5 to 24 hours) to perform binder removal, and further, predetermined conditions ( For example, baking is performed at 1000 to 1400 ° C. and 0.5 to 8 hours. By this firing, the varistor green layer L1 made of the first green sheet becomes the varistor part 7, the support green layer L2 made of the second green sheet becomes the support part 9, and the varistor part 7 is sandwiched between the support parts 9. The element body 3 is obtained. The varistor green layer L1 and the support green layer L2 are integrally fired. After firing, the element body 3 may be subjected to barrel polishing as necessary. The barrel polishing may be performed before firing, that is, after cutting the stacked body LB.

  Next, a conductive paste is applied so as to cover both end faces 3a and 3b of the element body 3, and the conductive paste is baked on the element body 3 by heat treatment to form a first electrode layer. Thereafter, the second and third electrode layers are formed by performing an electroplating process such as Ni plating and Sn plating so as to cover the first electrode layer. As a result, the terminal electrodes 5 are formed on both end sides of the element body 3. As the conductive paste, for example, a metal powder mixed with glass frit and an organic vehicle can be used. As the metal powder, for example, a material mainly composed of Cu, Ag, or an Ag—Pd alloy can be used.

  Next, at least one element selected from the group consisting of alkali metals (for example, Li, Na, etc.), Ag, and Cu is diffused from the exposed surface (four side surfaces 3c to 3f) of the element body 3. Here, an example in which an alkali metal element is diffused will be described.

  First, an alkali metal compound is attached to the surface (four side surfaces 3c to 3f) of the element body 3 on which the terminal electrode 5 is formed. A sealed rotating pot can be used for adhesion of the alkali metal compound. Although it does not specifically limit as an alkali metal compound, It is a compound which an alkali metal can diffuse from the surface of the element | base_body 3 by heat processing, and an alkali metal oxide, hydroxide, chloride, nitrate, borate, carbonic acid Salts and oxalates are used.

  And the element | base_body 3 to which this alkali metal compound has adhered is heat-processed by predetermined temperature and time with an electric furnace. As a result, the alkali metal diffuses from the surface of the element body 3 (four side surfaces 3c to 3f) to the inside from the alkali metal compound. A preferable heat treatment temperature is 700 to 1000 ° C., and the heat treatment atmosphere is air. The heat treatment time (holding time) is preferably 10 minutes to 4 hours.

  In the element body 3 (varistor portion 7 and support portion 9), the portion where the alkali metal element is diffused, that is, the first regions 8a and 10a where the alkali metal element is present, has high resistance and low capacitance as described above. Figured. Since the end faces 3a and 3b (end faces 7e and 7f of the varistor part 7) of the element body 3 are covered with the terminal electrode 5, the alkali metal element does not diffuse from the end faces 3a and 3b. Therefore, the alkali metal element does not hinder the electrical connection between the terminal electrode 5 and the varistor part 7.

  By these processes, the chip varistor 1 is obtained.

  As described above, in this embodiment, the varistor part 7 extends between the pair of end surfaces 3 a and 3 b so that the varistor part 7 is connected to the terminal electrode 5, and the varistor part 7 directly exhibits the varistor characteristics between the terminal electrodes 5. Functions as a region to express. That is, unlike the so-called multilayer chip varistor, the chip varistor 1 exhibits varistor characteristics between the terminal electrodes 5 without providing an internal electrode. For this reason, even when a surge voltage such as ESD is applied, a portion where the electric field distribution is concentrated does not occur in the varistor portion 7, and the ESD tolerance does not decrease.

  In the present embodiment, the varistor portion 7 includes a first region 8a in which at least one element selected from the group consisting of alkali metal, Ag, and Cu is present. The first region 8a has a lower electrical conductivity and a lower dielectric constant than the second region 8b in which an element selected from the group consisting of alkali metal, Ag, and Cu does not exist. Therefore, when the varistor part 7 includes the first region 8a, the electrostatic capacity of the varistor part 7 is reduced, and the electrostatic capacity of the chip varistor 1 can be reduced.

  In the multilayer chip varistor, the area of the portion where the internal electrodes overlap may vary due to factors such as the accuracy of electrode pattern formation on the varistor green sheet, misalignment of the varistor green sheet, or misalignment of the laminate. . When the area of the portion where the internal electrodes overlap each other varies, the capacitance generated by the portion where the internal electrodes overlap each other varies. On the other hand, since the chip varistor 1 does not include the internal electrode as described above, there is no variation in capacitance caused by the internal electrode.

  In the present embodiment, the support portion 9 is positioned so as to sandwich the varistor portion 7 in a direction orthogonal to the facing direction of the end surfaces 3a and 3b (end surfaces 9e and 9f). Thereby, the varistor part 7 can be reliably protected by the support part 9.

  In the present embodiment, the first region 8a of the varistor portion 7 is formed on the varistor portion 7 so as to sandwich both sides of the second region 8b of the varistor portion 7 when viewed from the opposing direction of the end surfaces 3a, 3b (end surfaces 7e, 7f). It is located on the outer surface (side surfaces 7c, 7d) side. Since the electric conductivity on the outer surface (side surfaces 7c, 7d) side of the varistor portion 7 is low, the surface current hardly flows on the outer surfaces (side surfaces 7c, 7d) of the varistor portion 7. As a result, the chip varistor 1 can suppress the occurrence of leakage current.

  In the present embodiment, the element selected from the group consisting of alkali metal, Ag, and Cu is diffused from both side surfaces 7c, 7d extending in the opposing direction of the end surfaces 3a, 3b (end surfaces 9e, 9f) in the varistor portion 7. Therefore, it exists in the first region 8a. Since at least one element selected from the group consisting of alkali metal, Ag, and Cu is diffused from the outer surface of the element body 3, at least one element selected from the group consisting of alkali metal, Ag, and Cu Can be easily controlled.

  In the present embodiment, the support portion 9 also includes the first region 10a in which at least one element selected from the group consisting of alkali metal, Ag, and Cu is present, and the capacitance is reduced. The electrostatic capacity of the chip varistor 1 can be represented by the sum of the electrostatic capacity of each of the varistor part 7 and the support part 9 that are located between the terminal electrodes 5. Therefore, the electrostatic capacity of the chip varistor 1 can be further reduced.

  In this embodiment, the support part 9 containing ZnO as a main component contains Zr as a subcomponent. Zr acts as a substance that suppresses grain growth of ZnO. For this reason, in the support part 9, the grain growth of ZnO is suppressed and the crystal grain of ZnO is comparatively small as FIG. 7 shows. The average crystal grain size of the varistor part 7 determined by the cutting method is 10 to 30 μm, and the average crystal grain size of the support part 9 is 1 to 3 μm. The cutting method is a crystal in which an arbitrary line segment crossing the crystal is drawn on a photograph taken with an electron microscope of about 1000 to 5000 times, and the length of the arbitrary line segment intersects with the arbitrary line segment. The average value is obtained by dividing by the number of. The average value obtained by the cutting method is taken as the average crystal grain size.

  In the varistor part 7, Zr does not contain anything other than contamination caused by raw materials or processes, so the ZnO crystal grains are relatively large. When the content of Zr is more than 20 atomic%, the sintering tends to be insufficient. When the content is less than 0.1 atomic%, ZnO tends to grow. Therefore, the Zr content in the support portion 9 is preferably in the range of 0.1 to 20 atomic%.

  The electric resistance value of the ZnO crystal grain boundary is much larger than that of the ZnO crystal grain, and the electric field is mainly applied to the ZnO crystal grain boundary. For this reason, the electrostatic capacity developed in the sintered body made of ZnO crystal grains is affected by the number of ZnO crystal grain boundaries between the terminal electrodes 5. That is, when the number of ZnO crystal grain boundaries between the terminal electrodes 5 is small, the capacitance is high, and when the number of ZnO crystal grain boundaries between the terminal electrodes 5 is large, the capacitance is low.

  As described above, in the chip varistor 1, since the ZnO grain growth is suppressed and the ZnO crystal grains are relatively small in the support portion 9, the number of ZnO crystal grain boundaries between the terminal electrodes 5 is relatively large. . On the other hand, in the varistor portion 7, the ZnO crystal grains are relatively large, and the number of ZnO crystal grain boundaries between the terminal electrodes 5 is relatively small. As a result, the electrostatic capacity of the support portion 9 is lowered, and the electrostatic capacity of the chip varistor 1 can be reduced. In the support portion 9, as described above, the number of ZnO crystal grain boundaries between the terminal electrodes 5 is relatively large. For this reason, in the support part 9, a varistor voltage becomes very high and the support part 9 does not substantially function as a varistor.

  In this embodiment, the support part 9 contains Sr as a subcomponent. Since Sr forms a liquid phase during firing, it functions as a glue that connects the main surfaces 7a and 7b of the varistor portion 7 and the main surfaces 9a and 9b of the support portion. Therefore, the connection strength at the interface between the varistor part 7 and the support part 9 becomes strong, and the occurrence of peeling between the varistor part 7 and the support part 9 can be suppressed. When the content of Sr is more than 30 atomic%, it tends to be melted. When the content is less than 0.1 atomic%, the sintering is insufficient and peeling occurs between the varistor part 7 and the support part 9. Tend to occur. Therefore, the Sr content in the support portion 9 is preferably in the range of 0.1 to 30 atomic%.

  In this embodiment, the support part 9 contains Co as a subcomponent. If the content of Co is more than 50 atomic%, it diffuses into the varistor part 7 and the varistor voltage of the varistor part 7 increases, which is not suitable for practical use. If the Co content is less than 0.05 atomic%, Co diffuses from the varistor part 7 and the non-linearity of the varistor part 7 tends to deteriorate. Therefore, the content of Co in the support portion 9 is preferably in the range of 0.05 to 50 atomic%. It is preferable that the Co contents in the varistor part 7 and the support part 9 are approximated so as not to deteriorate the characteristics.

  The preferred embodiments of the present invention have been described above. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

  The varistor part 7 may further contain Sr as a subcomponent. In this case, the connection strength at the interface between the varistor part 7 and the support part 9 is further strengthened, and the occurrence of peeling between the varistor part 7 and the support part 9 can be further suppressed.

  The support part 9 may contain a rare earth metal element as a subcomponent in addition to the components described above. As described above, since the support portion 9 contains Zr, the number of ZnO crystal grain boundaries between the terminal electrodes 5 increases, and the varistor voltage becomes very high. Therefore, even if the support portion 9 contains a rare earth metal element, the support portion 9 does not substantially exhibit varistor characteristics and does not function as a varistor.

  The support portion 9 does not necessarily include the first region 10a in which at least one element selected from the group consisting of alkali metal, Ag, and Cu is present. That is, at least one element selected from the group consisting of alkali metal, Ag, and Cu may not be present in the support portion 9. Conversely, the entire support portion 9 may be a region where at least one element selected from the group consisting of alkali metals, Ag, and Cu is present.

  DESCRIPTION OF SYMBOLS 1 ... Chip varistor, 3 ... Element body, 3a, 3b ... End surface, 3c-3f ... Side surface, 5 ... Terminal electrode, 7 ... Varistor part, 7a, 7b ... Main surface, 7c, 7d ... Side surface, 7e, 7f ... End surface 8a ... 1st area | region, 8b ... 2nd area | region, 9 ... Support part, 9a, 9b ... Main surface, 9c, 9d ... Side surface, 9e, 9f ... End face, 10a ... 1st area | region, 10b ... 2nd area | region.

Claims (6)

A chip varistor comprising: an element body including a pair of end faces facing each other; and a terminal electrode disposed on each of the end faces of the element body,
The prime field is
A varistor portion comprising a sintered body mainly composed of ZnO, extending between the pair of end faces so as to be connected to the terminal electrode, and expressing a voltage nonlinear characteristic;
It is made of a sintered body containing ZnO as a main component, extends between the pair of end faces so as to be connected to the terminal electrode, and is positioned with the varistor portion sandwiched in a direction perpendicular to the opposing direction of the pair of end faces. A support part,
The varistor portion includes a first region where at least one element selected from the group consisting of alkali metal, Ag, and Cu is present, and an alkali metal extending between the pair of end faces so as to be connected to the terminal electrode, A second region in which an element selected from the group consisting of Ag and Cu does not exist,
In the first region, at least one element selected from the group consisting of alkali metal, Ag, and Cu is dissolved in the crystal grains of ZnO, and the first region is compared with the second region. A chip varistor characterized in that the electrical conductivity of ZnO crystal grains is low and the capacitance is low .   The first region of the varistor portion is located on the outer surface side of the varistor portion so as to sandwich both sides of the second region of the varistor portion when viewed from the opposing direction of the pair of end faces. The chip varistor according to claim 1.   The element selected from the group consisting of alkali metal, Ag, and Cu is present in the first region by being diffused from both side surfaces extending in the opposing direction of the pair of end surfaces in the varistor portion. The chip varistor according to claim 2.   The chip varistor according to any one of claims 1 to 3, wherein the support portion includes a region in which at least one element selected from the group consisting of an alkali metal, Ag, and Cu is present. .   The chip varistor according to any one of claims 1 to 4, wherein the support part contains Sr, Zr, and Co as subcomponents. The chip varistor according to claim 5, wherein the varistor portion further contains Sr as a subcomponent.

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