Transient Voltage Protection Devices

Abstract

To provide a transient voltage protection device that can prevent a reduction in the durability of the transient voltage protection device and improve transient voltage protection characteristics.SOLUTION: A transient voltage protection device 1 comprises: an element assembly 2; external electrodes 3, 4 that are arranged on the element assembly 2; an internal electrode 5 that is arranged in the element assembly 2 and connected with the external electrode 3; and an internal electrode 6 that is arranged in the element assembly 2 and connected with the external electrode 4. The internal electrode 5 has a principal surface 5c. The internal electrode 6 has a principal surface 6c facing the principal surface 5c. The element assembly 2 has a cavity S formed in a portion located between the principal surface 5c and the principal surface 6c. The positions of a pair of opening ends S1, S2 of the cavity S in a third direction D3 are defined by the principal surface 5c and the principal surface 6c, respectively. The pair of opening ends S1, S2 are different in opening space from each other.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a transient voltage protection device. [Background technology]

[0002] A known transient voltage protection device includes an element body, a pair of external electrodes disposed on the element body, and a pair of internal electrodes disposed within the element body so as to face each other (see, for example, Patent Document 1). Each internal electrode is connected to a corresponding one of the pair of external electrodes. Tips of the pair of internal electrodes face each other within a cavity formed inside the element body. The transient voltage is caused, for example, by electrostatic discharge (ESD). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2012 / 050073 Summary of the Invention [Problem to be solved by the invention]

[0004] In the transient voltage protection device described above, the tips of the pair of internal electrodes face each other. Discharge occurs mainly between the tips of the pair of internal electrodes. In a configuration in which the tips of the pair of internal electrodes face each other, an electric field tends to concentrate at the tips, making discharge more likely to occur between the pair of internal electrodes. This configuration can promote discharge and improve transient voltage protection characteristics.

[0005] However, repeated discharges tend to damage the tips of the internal electrodes. If the tips of the internal electrodes are damaged, discharges become difficult to generate, and the transient voltage protection characteristics may deteriorate. Therefore, a configuration in which the tips of a pair of internal electrodes face each other may reduce the durability of the transient voltage protection device.

[0006] An object of one aspect of the present invention is to provide a transient voltage protection device that can suppress a decrease in durability of the transient voltage protection device and improve transient voltage protection characteristics. [Means for solving the problem]

[0007] A transient voltage protection device according to one embodiment includes an element body, first and second external electrodes disposed on the element body, a first internal electrode disposed within the element body and connected to the first external electrode, and a second internal electrode disposed within the element body and connected to the second external electrode. The first internal electrode has a first main surface. The second internal electrode has a second main surface opposite to the first main surface. A cavity is formed in a portion of the element body located between the first and second main surfaces. The positions of a pair of open ends of the cavity in the direction in which the first and second main surfaces face each other are defined by the first and second main surfaces, respectively. The opening areas of the pair of open ends are different from each other.

[0008] In one of the above embodiments, the positions of a pair of open ends of the cavity in the direction in which the first main surface and the second main surface face each other are defined by the first main surface and the second main surface, respectively. That is, the first main surface and the second main surface include regions exposed to the cavity. The opening areas of the pair of open ends are different from each other. That is, the area of ​​the region of the first main surface exposed to the cavity and the area of ​​the region of the second main surface exposed to the cavity are different from each other. Hereinafter, the region of the first main surface exposed to the cavity may be referred to as the "first region," and the region of the second main surface exposed to the cavity may be referred to as the "second region." For example, in a configuration in which the area of ​​the first region is smaller than the area of ​​the second region, the electric field tends to concentrate in the first region, and discharge tends to occur between the first region and the second region. Even in a configuration in which the area of ​​the second region is smaller than the area of ​​the first region, the electric field tends to concentrate in the second region, and discharge tends to occur between the first region and the second region. Therefore, the above-described one aspect can promote discharge and improve transient voltage protection characteristics. In a configuration in which the area of ​​the first region is smaller than the area of ​​the second region, the area of ​​the second region is larger than the area of ​​the first region. Even if discharges are repeated, a configuration in which the area of ​​the second region is larger than the area of ​​the first region makes it difficult to damage the entire second region. In a configuration in which the area of ​​the second region is smaller than the area of ​​the first region, the area of ​​the first region is larger than the area of ​​the second region. Even if discharges are repeated, a configuration in which the area of ​​the first region is larger than the area of ​​the second region makes it difficult to damage the entire first region. Therefore, the above-mentioned one aspect suppresses a decrease in the durability of the transient voltage protection device.

[0009] In the above-mentioned one aspect, the cavity may not overlap with the periphery of the first main surface and the periphery of the second main surface when viewed in the direction in which the first main surface and the second main surface face each other. In a configuration in which the cavity does not overlap the periphery of the first principal surface and the periphery of the second principal surface when viewed in the direction in which the first principal surface and the second principal surface face each other, an electric field is unlikely to concentrate at the periphery of the first principal surface and the periphery of the second principal surface, and discharge is unlikely to occur between the peripheries. Therefore, discharge is sure to occur between the first region of the first principal surface and the second region of the second principal surface. This configuration can further suppress a decrease in durability of the transient voltage protection device and surely improve the transient voltage protection characteristics.

[0010] In the above-described one aspect, the element body may have a discharge auxiliary part in contact with the first principal surface and the second principal surface. The discharge auxiliary part may form a side wall that defines the cavity so as to connect the pair of open ends. In a configuration in which the discharge auxiliary portion forms a sidewall that defines a cavity so as to connect the pair of open ends, discharge is reliably generated between the first main surface (first region) and the second main surface (second region), and therefore this configuration can reliably improve transient voltage protection characteristics.

[0011] In the one aspect described above, the discharge auxiliary portion may be located between the first main surface and the second main surface so as to constitute the entire side wall. In a configuration in which the discharge auxiliary portion is located between the first and second main surfaces so as to constitute the entire side wall, discharge occurs more reliably between the first main surface (first region) and the second main surface (second region), and therefore this configuration can more reliably improve transient voltage protection characteristics.

[0012] In one of the above aspects, the discharge auxiliary portion may not be in contact with the end of the first main surface located opposite the end connected to the first external electrode and the end of the second main surface located opposite the end connected to the second external electrode. In a configuration in which the discharge auxiliary portion does not contact the edges of the first and second principal surfaces, an electric field is less likely to concentrate at the edges of the first and second principal surfaces, and discharge is less likely to occur between the peripheries. Therefore, discharge is reliably generated between the first principal surface (first region) and the second principal surface (second region). This configuration can further suppress a decrease in durability of the transient voltage protection device and reliably improve the transient voltage protection characteristics. [Effects of the Invention]

[0013] One aspect of the present invention provides a transient voltage protection device that can suppress a decrease in durability of the transient voltage protection device and improve transient voltage protection characteristics. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view illustrating a transient voltage protection device according to one embodiment. [Figure 2] FIG. 2 is a diagram showing a cross-sectional configuration of a transient voltage protection device. [Figure 3] FIG. 3 is a diagram showing a cross-sectional configuration of a transient voltage protection device. [Figure 4] FIG. 4 is an exploded perspective view showing the internal electrode and the discharge auxiliary portion. [Figure 5] FIG. 5 is a plan view showing the configuration of the internal electrodes and the discharge auxiliary parts. [Figure 6] FIG. 6 is a diagram showing a cross-sectional configuration of a transient voltage protection device according to a modified example of this embodiment. [Figure 7]FIG. 7 is a diagram showing a cross-sectional configuration of a transient voltage protection device according to this modification. [Figure 8] FIG. 8 is a plan view showing the configuration of the internal electrodes and the discharge auxiliary parts. [Figure 9] FIG. 9 is a plan view showing the configuration of the internal electrodes and the discharge auxiliary parts. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same functions will be denoted by the same reference numerals, and redundant description will be omitted.

[0016] The configuration of a transient voltage protection device 1 according to this embodiment will be described with reference to Figures 1 to 5. Figure 1 is a perspective view showing the transient voltage protection device according to this embodiment. Figures 2 and 3 are views showing the cross-sectional configuration of the transient voltage protection device. Figure 4 is an exploded perspective view showing the internal electrodes and discharge auxiliary units. Figure 5 is a plan view showing the configuration of the internal electrodes and discharge auxiliary units. As shown in FIGS. 1 and 2, the transient voltage protection device 1 includes a body 2, a plurality of external electrodes 3 and 4, and a plurality of internal electrodes 5 and 6. In this embodiment, the transient voltage protection device 1 includes two external electrodes 3 and 4 and two internal electrodes 5 and 6. The transient voltage protection device 1 is mounted in an electronic device (not shown). The transient voltage protection device 1 protects the electronic device from transient voltages. The electronic device protected by the transient voltage protection device 1 includes, for example, a circuit board or an electronic component. The transient voltage is caused by, for example, ESD.

[0017] The element body 2 has a rectangular parallelepiped shape. Examples of rectangular parallelepiped shapes include a rectangular parallelepiped shape with chamfered corners and ridges, and a rectangular parallelepiped shape with rounded corners and ridges. The element body 2 has a pair of end faces 2a, 2b facing each other, a pair of side faces 2c, 2d facing each other, and a pair of side faces 2e, 2f facing each other. In this embodiment, the pair of end faces 2a, 2b face each other in a first direction D1, the pair of side faces 2e, 2f face each other in a second direction D2, and the pair of side faces 2c, 2d face each other in a third direction D3. The pair of end faces 2a, 2b and the four side faces 2c, 2d, 2e, 2f form the outer surface of the element body 2. The four side surfaces 2c, 2d, 2e, and 2f are adjacent to the end surface 2a and the end surface 2b, respectively, and extend in the first direction D1 to connect the end surface 2a and the end surface 2b. One of the four side surfaces 2c, 2d, 2e, and 2f is defined as a mounting surface that faces an electronic device in which the transient voltage protection device 1 is mounted.

[0018] As shown in Figures 2 and 3, the element body 2 has an element body main body 20. The element body main body 20 is configured by stacking multiple insulator layers in the third direction D3. The element body main body 20 has multiple stacked insulator layers. In the element body main body 20, the insulator layers are integrated to the extent that the boundaries between the insulator layers are not visible. Each insulator layer is configured, for example, from a sintered ceramic green sheet containing an insulating material. The insulating material may include, for example, a ceramic material. The ceramic material may be selected from the group consisting of Fe2O3, NiO, CuO, ZnO, MgO, SiO2, TiO2, MnCO3, SrCO3, CaCO3, BaCO3, Al2O3, ZrO2, and BO3. The insulating layer may be made of a single ceramic material or two or more ceramic materials. The insulating layer may contain glass. The insulating layer may contain copper oxide (CuO or Cu2O) to enable low-temperature sintering.

[0019] The first direction D1 is the length direction of the element body 2, the second direction D2 is the width direction of the element body 2, and the third direction D3 is the height direction of the element body 2. The length of the element body 2 is, for example, not less than 0.2 mm and not more than 2.0 mm. The width of the element body 2 is, for example, not less than 0.2 mm and not more than 1.2 mm. The height of the element body 2 is, for example, not less than 0.2 mm and not more than 1.2 mm. In this embodiment, the length of the element body 2 is 1.6 mm, the width of the element body 2 is 0.8 mm, and the height of the element body 2 is 0.8 mm.

[0020] The external electrodes 3 and 4 are arranged on the element body 2. The external electrodes 3 and 4 are arranged on the element body 2 so as to face each other in the first direction D1. The external electrodes 3 and 4 are arranged at both ends of the element body 2 in the first direction D1. The external electrodes 3 and 4 are spaced apart from each other in the first direction D1. For example, when the external electrode 3 constitutes a first external electrode, the external electrode 4 constitutes a second external electrode.

[0021] The external electrode 3 is disposed on the end face 2a and connected to the internal electrode 5. The external electrode 3 is physically and electrically connected to the internal electrode 5. The external electrode 3 covers the end face 2a. The external electrode 3 also covers a portion of each of the four side faces 2c, 2d, 2e, and 2f. Each portion of the four side faces 2c, 2d, 2e, and 2f that is covered by the external electrode 3 is located closer to the end face 2a on the corresponding side face 2c, 2d, 2e, and 2f. The external electrode 3 is disposed over the entire end face 2a and on the ends of the side faces 2c, 2d, 2e, and 2f that are closer to the end face 2a.

[0022] The external electrode 4 is disposed on the end face 2b and connected to the internal electrode 6. The external electrode 4 is physically and electrically connected to the internal electrode 6. The external electrode 4 covers the end face 2b. The external electrode 4 also covers a portion of each of the four side faces 2c, 2d, 2e, and 2f. Each portion of the four side faces 2c, 2d, 2e, and 2f that is covered by the external electrode 4 is located closer to the end face 2b on the corresponding side face 2c, 2d, 2e, and 2f. The external electrode 4 is disposed over the entire end face 2b and on the ends of the side faces 2c, 2d, 2e, and 2f that are closer to the end face 2b.

[0023] The internal electrodes 5 and 6 are arranged in the element body 2 so as to face each other in the third direction D3. The internal electrodes 5 and 6 extend in the first direction D1. The internal electrode 5 is arranged closer to the side surface 2d. The internal electrode 6 is arranged closer to the side surface 2c. The internal electrodes 5 and 6 are arranged at different height positions in the third direction D3. The internal electrode 5 is exposed at the end surface 2a, but is not exposed at the end surface 2b or the side surfaces 2c, 2d, 2e, or 2f. The internal electrode 6 is exposed at the end surface 2b, but is not exposed at the end surface 2a or the side surfaces 2c, 2d, 2e, or 2f. For example, if the internal electrode 5 constitutes a first internal electrode, the internal electrode 6 constitutes a second internal electrode.

[0024] 2 to 5, the internal electrode 5 has a pair of ends 5a, 5b, a pair of opposing main surfaces 5c, 5d, and a pair of opposing side edges 5e, 5f. The main surface 5c faces the internal electrode 6. Each of the side edges 5e, 5f may form a surface. The internal electrode 5 is spaced apart from the end surface 2b and the side surfaces 2c, 2d, 2e, and 2f. End 5a is exposed at end face 2a. End 5a is connected to external electrode 3. In this embodiment, end 5a is directly connected to external electrode 3. End 5a constitutes a connection end connected to external electrode 3. End 5b is located opposite end 5a. End 5b is located within element body 2 and is not exposed on the outer surface of element body 2. End 5b is spaced apart from each end face 2a, 2b. End 5b is buried in element body 2 and is in contact only with element body 2. End 5b is not exposed from element body 2 and is covered by element body 2. When viewed from third direction D3, end 5b is spaced apart from external electrode 4 and does not overlap with external electrode 4.

[0025] 2 to 5, the internal electrode 6 has a pair of ends 6a, 6b, a pair of opposing main surfaces 6c, 6d, and a pair of opposing side edges 6e, 6f. The main surface 6c faces the internal electrode 5 (main surface 5c). Each of the side edges 6e, 6f may form a surface. The internal electrode 6 is spaced from the end surface 2a and the side surfaces 2c, 2d, 2e, and 2f. The end 6a is exposed at the end face 2b. The end 6a is connected to the external electrode 4. In this embodiment, the end 6a is directly connected to the external electrode 4. The end 6a constitutes a connection end connected to the external electrode 4. The end 6b is located on the opposite side to the end 6a. The end 6b is located within the element body 2 and is not exposed on the outer surface of the element body 2. The end 6b is spaced apart from the end faces 2a, 2b. The end 6b is buried in the element body 2 and is in contact only with the element body 2. The end 6b is not exposed from the element body 2 and is covered by the element body 2. When viewed from the third direction D3, the end 6b is spaced apart from the external electrode 3 and does not overlap with the external electrode 3. For example, when the main surface 5c constitutes the first main surface, the main surface 6c constitutes the second main surface.

[0026] The external electrodes 3, 4 and the internal electrodes 5, 6 contain a conductive material. The conductive material may include, for example, Ag, Pd, Au, Pt, Cu, Ni, Al, Mo, or W. The conductive material may include, for example, an Ag / Pd alloy, an Ag / Cu alloy, an Ag / Au alloy, or an Ag / Pt alloy. The external electrodes 3, 4 and the internal electrodes 5, 6 may contain the same conductive material. The external electrodes 3, 4 and the internal electrodes 5, 6 may also contain different conductive materials. The external electrodes 3, 4 are formed, for example, by baking a conductive paste applied to the outer surface of the element body 2. The conductive paste for forming the external electrodes 3, 4 contains the above-mentioned conductive material. The internal electrodes 5, 6 are formed, for example, by applying the above-mentioned conductive paste to the ceramic green sheets and firing the same together with the ceramic green sheets. The conductive paste is applied to the ceramic green sheets by, for example, printing. The conductive paste for forming the internal electrodes 5, 6 also contains the above-mentioned conductive material.

[0027] As shown in Figures 2 to 5, the element body 2 has a discharge auxiliary part 21. In this embodiment, the number of discharge auxiliary part 21 is "1". The discharge auxiliary part 21 is arranged inside the element body 2 so as to be continuous with the element body main body part 20. The discharge auxiliary part 21 is spaced apart from the outer surface of the element body 2. The discharge auxiliary part 21 includes a pair of surfaces 21a, 21b facing each other, and an outer peripheral surface 21c. In this embodiment, the pair of surfaces 21a, 21b face each other in the third direction D3. The outer peripheral surface 21c is in contact with the element body main body part 20. The discharge auxiliary part 21 has an outer shape of a column. The outer shape of the discharge auxiliary part 21 may have an outer shape of a frustum. The discharge auxiliary part 21 has a through hole formed therein that penetrates the discharge auxiliary part 21 in the third direction D3. The through hole opens to each of the pair of faces 21a, 21b. Therefore, the discharge auxiliary part 21 also includes an inner circumferential face 21d. The outer circumferential face 21c and the inner circumferential face 21d are adjacent to the pair of faces 21a, 21b, respectively, and connect the faces 21a and 21b. In this embodiment, the discharge auxiliary part 21 has an outer shape of a column. The outer shape of the discharge auxiliary part 21 may have an outer shape of a polygonal column. When the outer shape of the discharge auxiliary part 21 has an outer shape of a polygonal column, the outline of the discharge auxiliary part 21 has a polygonal shape in a cross section perpendicular to the third direction D3. The height of the discharge auxiliary portion 21 is, for example, not less than 3 μm and not more than 20 μm. In this embodiment, the height of the discharge auxiliary portion 21 is 10 μm. The height of the discharge auxiliary portion 21 is defined by the length in the third direction D3.

[0028] 2 to 4, the discharge auxiliary part 21 is located between the pair of internal electrodes 5, 6 in the third direction D3. The surface 21a is in contact with the main surface 5c, and the surface 21b is in contact with the main surface 6c. The internal electrodes 5, 6 are connected to each other via the discharge auxiliary part 21. As shown in FIG. 5 , in this embodiment, the entire discharge auxiliary portion 21 overlaps with each of the internal electrodes 5 and 6 when viewed from the third direction D3. When viewed from the third direction D3, the discharge auxiliary portion 21 is spaced apart from the periphery of each of the internal electrodes 5 and 6. The periphery of the internal electrode 5 is defined by a pair of ends 5a and 5b and a pair of side edges 5e and 5f. The periphery of the internal electrode 6 is defined by a pair of ends 6a and 6b and a pair of side edges 6e and 6f. The discharge auxiliary portion 21 does not contact the end 5b of the internal electrode 5 or the end 6b of the internal electrode 6. The discharge auxiliary portion 21, together with the internal electrodes 5 and 6, constitutes a transient voltage suppressor. The transient voltage suppressor has transient voltage absorption capabilities.

[0029] The discharge auxiliary part 21 includes an insulating material and metal particles. The insulating material includes, for example, a ceramic material. The ceramic material is selected from the group consisting of, for example, Fe2O3, NiO, CuO, ZnO, MgO, SiO2, TiO2, MnCO3, SrCO3, CaCO3, BaCO3, Al2O3, ZrO2, and B2O3. The discharge auxiliary part 21 may include only one ceramic material selected from this group, or may include two or more ceramic materials selected from this group. The metal particles include, for example, Ag, Pd, Au, Pt, Ag / Pd alloy, Ag / Cu alloy, Ag / Au alloy, or Ag / Pt alloy. The discharge auxiliary part 21 may include semiconductor particles. The semiconductor particles may be made of, for example, RuO2. The discharge auxiliary part 21 may also include glass. The discharge auxiliary portion 21 is formed, for example, by applying a slurry to the ceramic green sheet and firing the ceramic green sheet together with the ceramic green sheet. The slurry contains the ceramic material and metal particles. The slurry is applied to the ceramic green sheet by, for example, printing.

[0030] As shown in FIGS. 2 to 5, a cavity S is formed inside the element body 2. The cavity S is formed in a portion of the element body 2 located between the main surface 5c and the main surface 6c. In this embodiment, the cavity S is formed in the discharge auxiliary portion 21 of the element body 2. The cavity S is not in communication with the outside of the element body 2. The cavity S is defined by the pair of internal electrodes 5, 6 and the element body 2. In this embodiment, the cavity S is defined by the pair of internal electrodes 5, 6 and the discharge auxiliary portion 21. The surfaces defining the cavity S include the main surface 5c of the internal electrode 5 and the main surface 6c of the internal electrode 6. The surfaces defining the cavity S include the inner circumferential surface 21d of the discharge auxiliary portion 21. The discharge auxiliary portion 21 defines a pair of opening ends S1, S2 of the cavity S in the third direction D3.

[0031] One of the pair of internal electrodes 5, 6 forms an upper wall that defines the cavity S. The other of the pair of internal electrodes 5, 6 forms a lower wall that defines the cavity S. The discharge auxiliary part 21 forms a side wall that defines the cavity S. The side wall formed by the discharge auxiliary part 21 defines the cavity S so as to connect the pair of opening ends S1, S2. The surface of the side wall formed by the discharge auxiliary part 21 includes an inner circumferential surface 21d of the discharge auxiliary part 21. In this embodiment, the entire surface of the side wall formed by the discharge auxiliary part 21 is formed by the inner circumferential surface 21d of the discharge auxiliary part 21. The discharge auxiliary part 21 is located between the internal electrode 5 (main surface 5c) and the internal electrode 6 (main surface 6c) so as to form the entire side wall.

[0032] As shown in FIG. 5, when viewed in the third direction D3, the cavity S is spaced from the periphery of the main surface 5c of the internal electrode 5 and the periphery of the main surface 6c of the internal electrode 6. When viewed in the third direction D3, the cavity S does not overlap with the peripheries of the main surfaces 5c and 6c. The periphery of the main surface 5c is defined by a pair of ends 5a, 5b and a pair of side edges 5e, 5f. The periphery of the main surface 6c is defined by a pair of ends 6a, 6b and a pair of side edges 6e, 6f. As shown in FIGS. 4 and 5, the pair of opening ends S1, S2 have, for example, a circular shape when viewed in the third direction D3. The circular shape includes a perfect circle, an oval shape, or an ellipse shape. The shape of the pair of opening ends S1, S2 is not limited to a circular shape. When viewed in the third direction D3, the shape of the pair of opening ends S1, S2 may be a polygonal shape. The voids S are formed, for example, by firing the organic lacquer applied to the ceramic green sheet together with the ceramic green sheet. The voids S are formed by burning off the organic lacquer. The organic lacquer contains an organic solvent and an organic binder. The organic lacquer is applied to the ceramic green sheet by, for example, printing.

[0033] The position of the open end S1 of the cavity S in the third direction D3 is determined by the main surface 5c. The open end S1 is covered by the main surface 5c. The open end S1 is in contact with the main surface 5c and spaced apart from the main surface 6c. The open end S1 is spaced apart from the ends 5a and 5b in the first direction D1. When viewed in the third direction D3, the open end S1 does not overlap with the periphery of the main surface 5c. The main surface 5c includes a region 5g exposed to the cavity S. The region 5g is spaced apart from the ends 5a and 5b in the first direction D1. When viewed in the third direction D3, the region 5g does not overlap with the periphery of the main surface 5c. The outline of the region 5g is defined by the open end S1. Therefore, the area of ​​the region 5g is defined by the opening area of ​​the open end S1. The region 5g covers the open end S1. The region 5g faces the internal electrode 6 in the third direction D3.

[0034] The position of the open end S2 of the cavity S in the third direction D3 is determined by the main surface 6c. The open end S2 is covered by the main surface 6c. The open end S2 is in contact with the main surface 6c and spaced apart from the main surface 5c. The open end S2 is spaced apart from the ends 6a and 6b in the first direction D1. When viewed in the third direction D3, the open end S2 does not overlap with the periphery of the main surface 6c. The main surface 6c includes a region 6g exposed to the cavity S. The region 6g is spaced apart from the ends 6a and 6b in the first direction D1. When viewed in the third direction D3, the region 6g does not overlap with the periphery of the main surface 6c. The outline of the region 6g is defined by the open end S2. Therefore, the area of ​​the region 6g is defined by the opening area of ​​the open end S2. The region 6g covers the open end S2. The region 6g faces the internal electrode 5 in the third direction D3.

[0035] The opening areas of the pair of opening ends S1, S2 are different from each other. When viewed from the third direction D3, the circumferential lengths of the pair of opening ends S1, S2 are different from each other. Therefore, the area of ​​region 5g and the area of ​​region 6g are different from each other. Region 5g and region 6g are exposed to cavity S with different areas from each other. Region 5g and region 6g directly face each other in the third direction D3 so that cavity S is located between region 5g and region 6g.

[0036] In this embodiment, the opening area of ​​the opening end S1 is smaller than the opening area of ​​the opening end S2. That is, the area of ​​the region 5g is smaller than the area of ​​the region 6g. The perimeter of the opening end S1 is smaller than the perimeter of the opening end S2. When viewed from the third direction D3, the opening end S1 is located inside the opening end S2. The opening area of ​​the opening end S2 may be smaller than the opening area of ​​the opening end S1. The opening area of ​​the opening end S1 (area of ​​the region 5g) is, for example, 0.0007 mm 2 More than 0.125mm 2 In this embodiment, the opening area of ​​the opening end S1 and the area of ​​the region 5g are 0.008 mm 2 is. The opening area of ​​the opening end S2 (area of ​​the region 6g) is, for example, 0.0008 mm 2 More than 0.180μm 2 In this embodiment, the opening area of ​​the opening end S2 and the area of ​​the region 6g are 0.03 μm 2 is.

[0037] The inner diameter of the discharge auxiliary part 21 is smallest at the opening end S1 and largest at the opening end S2. That is, the area of ​​the inner region of the discharge auxiliary part 21 is smallest at the opening end S1 and largest at the opening end S2. When the discharge auxiliary part 21 is cut along a plane perpendicular to the third direction D3, the area of ​​the inner region of the discharge auxiliary part 21 varies in the third direction D3. In this embodiment, the area of ​​the inner region of the discharge auxiliary part 21 gradually varies in the third direction D3. The area of ​​the inner region of the discharge auxiliary part 21 gradually increases in the direction from the internal electrode 5 (main surface 5c) to the internal electrode 6 (main surface 6c) in the third direction D3. The region defined by the inner circumferential surface 21d of the discharge auxiliary part 21 has a truncated cone shape. The area of ​​the inner region of the discharge auxiliary part 21 may vary stepwise in the third direction D3. The region defined by the inner circumferential surface 21d of the discharge auxiliary part 21 may have a truncated pyramid shape.

[0038] As described above, in the transient voltage protection device 1, the positions of the pair of open ends S1, S2 of the cavity S in the third direction D3 are defined by the principal surfaces 5c and 6c, respectively, and the areas of the pair of open ends S1, S2 are different from each other. That is, the area of ​​the region 5g included in the principal surface 5c and exposed to the cavity S is different from the area of ​​the region 6g included in the principal surface 6c and exposed to the cavity S. For example, in a transient voltage protection device 1 in which the area of ​​region 5g is smaller than the area of ​​region 6g, an electric field is likely to concentrate in region 5g, and discharge is likely to occur between regions 5g and 6g. Even in a transient voltage protection device 1 in which the area of ​​region 6g is smaller than the area of ​​region 5g, an electric field is likely to be generated in region 6g, and discharge is likely to occur between regions 5g and 6g. Therefore, the transient voltage protection device 1 can improve the transient voltage protection characteristics. In a transient voltage protection device 1 in which the area of ​​region 5g is smaller than the area of ​​region 6g, the area of ​​region 6g is larger than the area of ​​region 5g. Even when discharges are repeated, in a transient voltage protection device 1 in which the area of ​​region 6g is larger than the area of ​​region 5g, the entire region 6g is less likely to be damaged. In a transient voltage protection device 1 in which the area of ​​region 6g is smaller than the area of ​​region 5g, the area of ​​region 5g is larger than the area of ​​region 6g. Even when discharges are repeated, in a transient voltage protection device 1 in which the area of ​​region 5g is larger than the area of ​​region 6g, the entire region 5g is less likely to be damaged. Therefore, in the transient voltage protection device 1, a decrease in the durability of the transient voltage protection device 1 is suppressed.

[0039] When viewed in the third direction D3, the cavity S does not overlap with the periphery of the main surface 5c or the periphery of the main surface 6c. Therefore, discharge is reliably generated between the region 5g and the region 6g. As a result, the transient voltage protection device 1 can further suppress a decrease in durability of the transient voltage protection device 1 and reliably improve the transient voltage protection characteristics.

[0040] The discharge auxiliary portion 21 contacts the main surface 5c and the main surface 6c, and forms a sidewall that defines the cavity S so as to connect the pair of opening ends S1, S2. Therefore, in the transient voltage protection device 1, discharge is reliably generated between the region 5g and the region 6g. As a result, the transient voltage protection device 1 can reliably improve the transient voltage protection characteristics.

[0041] The discharge auxiliary portion 21 is located between the main surface 5c and the main surface 6c so as to form the entire side wall. Therefore, in the transient voltage protection device 1, discharge occurs more reliably between the region 5g and the region 6g. As a result, the transient voltage protection device 1 can more reliably improve the transient voltage protection characteristics.

[0042] Discharge auxiliary portion 21 is not in contact with end 5b and end 6b. Therefore, discharge reliably occurs between region 5g and region 6g in transient voltage protection device 1. As a result, transient voltage protection device 1 can reliably improve the transient voltage protection characteristics.

[0043] The external electrodes 3, 4 are arranged on the element body 2 so as to face each other in the first direction D1. Because the external electrodes 3, 4 are arranged at both ends of the element body 2 in the first direction D1, the external electrodes 3, 4 can be spaced apart from each other. Therefore, the transient voltage protection device 1 can suppress the occurrence of short circuits between the external electrodes 3, 4.

[0044] The configuration of a transient voltage protection device 31 according to one modification of this embodiment will be described with reference to Figures 6 to 8. Figure 6 is a diagram showing a cross-sectional configuration of the transient voltage protection device according to this modification. Figure 7 is a diagram showing a cross-sectional configuration of the transient voltage protection device according to this modification. Figure 8 is a plan view showing the configuration of the internal electrode and the discharge auxiliary portion. This modification differs from the above-described present embodiment in terms of the configuration of the discharge auxiliary portion 21 and the cavity S. The following mainly describes the differences between this modification and the above-described present embodiment.

[0045] Like the transient voltage protection device 1, the transient voltage protection device 31 includes an element body 2, a plurality of external electrodes 3 and 4, and a plurality of internal electrodes 5 and 6. In this modification, the transient voltage protection device 31 also includes two external electrodes 3 and 4 and two internal electrodes 5 and 6. The element body 2 includes an element body main body portion 20 and a plurality of discharge auxiliary portions 21. The plurality of discharge auxiliary portions 21 are in contact with the main surface 5c and the main surface 6c. When viewed from the third direction D3, the plurality of discharge auxiliary portions 21 are arranged two-dimensionally with the first direction D1 as the row direction and the second direction D2 as the column direction. The discharge auxiliary portions 21 are spaced apart from one another. As shown in FIG. 8 , in this modification, five discharge auxiliary portions 21 are arranged in the row direction and three discharge auxiliary portions 21 are arranged in the column direction. Therefore, in this modification, the number of the plurality of discharge auxiliary portions 21 is "15."

[0046] A plurality of cavities S are formed in a portion of the element body 2 located between the main surface 5c and the main surface 6c. The positions of a pair of opening ends S1, S2 of each cavity S in the third direction D3 are defined by the main surface 5c and the main surface 6c, respectively. In this modification, each cavity S is defined by the inner circumferential surface 21d of the corresponding discharge auxiliary part 21. That is, each cavity S is formed inside the corresponding discharge auxiliary part 21. Each cavity S is formed inside the corresponding discharge auxiliary part 21 among the plurality of discharge auxiliary parts 21 that are two-dimensionally arranged. As shown in FIG. 8, in this modification, the number of the plurality of cavities S is "15."

[0047] The configuration of a modified example of element body 2 will be described with reference to Fig. 9. Fig. 9 is a plan view showing the configuration of the internal electrodes and discharge auxiliary parts. This modified example differs from the modified examples shown in Figs. 6 to 8 in terms of the configuration of discharge auxiliary parts 21 and cavity S. The following mainly describes the differences between this modified example and the modified examples shown in Figs. 6 to 8.

[0048] The discharge auxiliary parts 21 are arranged in a plurality of positions along the first direction D1 and a plurality of positions along a direction intersecting the first direction D1 and the second direction D2. The positions of the discharge auxiliary parts 21 in the first direction D1 are specified so as to be staggered in the second direction D2. That is, when viewed from the third direction D3, the discharge auxiliary parts 21 are arranged in a staggered pattern. The discharge auxiliary parts 21 are arranged spaced apart from each other. As shown in FIG. 9, in this modified example, the number of the discharge auxiliary parts 21 is 13. Each cavity S is formed inside a corresponding one of the discharge auxiliary parts 21 that are arranged in a staggered pattern. As shown in Fig. 9, in this modified example, the number of the cavities S is "13".

[0049] In each modified example, the number of the discharge auxiliary parts 21 is not limited to the number described above. The number of the discharge auxiliary parts 21 may be more or less than the number in the modified example described above. The number of the cavities S may correspond to the number of the discharge auxiliary parts 21. In each cavity S, the opening areas of the pair of opening ends S1, S2 may be different from each other. In each cavity S, the size relationship between the opening areas of the pair of opening ends S1, S2 may be reversed.

[0050] The above describes embodiments and modifications of the present invention, but the present invention is not necessarily limited to the above-described embodiments and modifications, and various modifications are possible without departing from the spirit of the present invention.

[0051] As viewed in the third direction D3, the cavity S may overlap with the periphery of the principal surface 5 c and the periphery of the principal surface 6 c. As described above, the transient voltage protection device 1 in which the cavity S does not overlap with the periphery of the principal surface 5 c and the periphery of the principal surface 6 c can further suppress a decrease in durability of the transient voltage protection device 1 and reliably improve the transient voltage protection characteristics.

[0052] In the transient voltage protection device 1, the element body 2 does not need to have the discharge auxiliary portion 21. A transient voltage protection device 1 in which the discharge auxiliary portion 21 forms the sidewall that defines the cavity S so as to connect the pair of opening ends S1, S2 in the element body 2 can reliably improve the transient voltage protection characteristics, as described above. In a configuration in which the element body 2 does not have the discharge auxiliary portion 21, the element body main body portion 20 forms the sidewall that defines the cavity S so as to connect the pair of opening ends S1, S2. In the transient voltage protection device 1, the discharge auxiliary portion 21 does not have to be located between the main surface 5c and the main surface 6c so as to form the entire side wall. A transient voltage protection device 1 in which the discharge auxiliary portion 21 forms the entire side wall can more reliably improve the transient voltage protection characteristics, as described above. In a configuration in which the discharge auxiliary portion 21 does not form the entire side wall, the element main body portion 20 is located between the main surface 5c and the main surface 6c so as to form part of the side wall. In this case, the remainder of the side wall is formed by the discharge auxiliary portion 21. In the transient voltage protection device 1, the discharge auxiliary part 21 may be in contact with the end 5b and the end 6b. As described above, a transient voltage protection device 1 in which the discharge auxiliary part 21 is not in contact with the end 5b and the end 6b can reliably improve the transient voltage protection characteristics.

[0053] In the transient voltage protection device 1, the internal electrodes 5 and 6 have the same shape, but may have different shapes. In the transient voltage protection device 1, the discharge auxiliary portion 21 and the cavity S are arranged in the second direction D2, i.e., approximately at the center of the width direction of the element body 2, but may also be arranged closer to the side surface 2f or the side surface 2e than the center of the width direction of the element body 2. [Explanation of symbols]

[0054] 1...transient voltage protection device, 2...element body, 3,4...external electrodes, 5,6...internal electrodes, 5a,5b,6a,6b...ends, 5c,6c...main surfaces, 21...discharge auxiliary portion, D1...first direction, D2...second direction, D3...third direction, S...cavity, S1,S2...open ends.

Claims

1. The base body and first and second external electrodes disposed on the element body; a first internal electrode having a first main surface, disposed within the element body, and connected to the first external electrode; a second internal electrode having a second main surface facing the first main surface, the second internal electrode being disposed within the element body and connected to the second external electrode, The element body is an element body portion; a discharge auxiliary part including a pair of surfaces facing each other in a direction in which the first main surface and the second main surface face each other, the discharge auxiliary part being disposed within the element body so as to be continuous with the element body part and in contact with the first main surface and the second main surface, a through hole is formed in the discharge auxiliary part, the through hole passing through the discharge auxiliary part in the direction in which the first main surface and the second main surface face each other and opening in each of the pair of surfaces, a cavity is formed in a portion of the element body located between the first main surface and the second main surface, positions of a pair of opening ends of the cavity in the direction in which the first main surface and the second main surface face each other are defined by the first main surface and the second main surface, respectively; the discharge auxiliary portion includes an outer peripheral surface and an inner peripheral surface that are adjacent to the pair of surfaces and connect the pair of surfaces, and also forms a side wall that defines the cavity so as to connect the pair of opening ends; the outer circumferential surface is in contact with the element body portion, the surface of the side wall formed by the discharge auxiliary portion includes the inner circumferential surface, the discharge auxiliary portion is spaced from the peripheries of the first internal electrode and the second internal electrode when viewed from the direction in which the first main surface and the second main surface face each other, and is not in contact with an end of the first main surface located opposite to an end connected to the first external electrode and an end of the second main surface located opposite to an end connected to the second external electrode, A transient voltage protection device, wherein the pair of open ends have different opening areas.

2. 2. The transient voltage protection device of claim 1, wherein the cavity does not overlap with a peripheral edge of the first main surface and a peripheral edge of the second main surface when viewed in the direction in which the first main surface and the second main surface face each other.

3. The transient voltage protection device according to claim 1 or 2, wherein the discharge auxiliary portion is located between the first main surface and the second main surface so as to constitute the entire side wall.

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