Transient voltage protection device

Abstract

To provide a transient voltage protection device that can improve mechanical strength.SOLUTION: A transient voltage protection device 1 includes: an element body 2 formed with a cavity S inside; a pair of external electrodes disposed on the element body 2; and a pair of internal electrodes 5, 6 disposed in the element body 2 to oppose each other, each internal electrode being connected to a corresponding external electrode of the pair of external electrodes. The element body 2 includes a surface 21a and an inner wall surface 20b which define the cavity S and oppose each other. The pair of internal electrodes 5, 6 are exposed to the cavity S and disposed on the surface 21a. In a cross section along a direction in which the surface 21a and the inner wall surface 20b oppose each other, the shape of a contour of the surface 21a is different from the shape of a contour of the inner wall surface 20b.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Known transient voltage protection devices include a body, a pair of external electrodes disposed on the body, and a pair of internal electrodes disposed in the body so as to face each other (see, for example, Patent Document 1). A cavity is formed inside the body. The pair of internal electrodes are connected to the corresponding external electrodes of the pair of external electrodes and exposed to the cavity.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One aspect of the present invention aims to provide a transient voltage protection device that can improve mechanical strength.

Means for Solving the Problems

[0005] The inventors of the present invention conducted research on a transient voltage protection device that can improve mechanical strength. As a result, the inventors obtained the following findings and arrived at the present invention.

[0006] In transient voltage protection devices, cavities formed inside the main body affect the mechanical strength of the transient voltage protection device. The cavities are defined by a first inner wall surface and a second inner wall surface of the main body that are opposite to each other. The inventors focused on the first inner wall surface and the second inner wall surface. As a result, the inventors found that in a configuration where the contours of the first inner wall surface and the second inner wall surface have different shapes in a cross-section along the direction in which the first inner wall surface and the second inner wall surface are opposite to each other, the mechanical strength of the transient voltage protection device can be improved. That is, in a configuration where the contours of the first inner wall surface and the second inner wall surface have different shapes in a cross-section along the direction in which the first inner wall surface and the second inner wall surface are opposite to each other, the mechanical strength of the transient voltage protection device can be improved.

[0007] A transient voltage protection device according to one embodiment comprises a body, a pair of external electrodes disposed on the body, and a pair of internal electrodes disposed within the body so as to face each other. A cavity is formed inside the body. The pair of internal electrodes are each connected to the corresponding external electrode of the pair of external electrodes. The body has a first inner wall surface and a second inner wall surface that define the cavity and face each other. The pair of internal electrodes are exposed to the cavity and are disposed on the first inner wall surface. In a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contours of the first inner wall surface and the contours of the second inner wall surface have different shapes.

[0008] In the above embodiment, in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contours of the first inner wall surface and the contours of the second inner wall surface exhibit different shapes. Therefore, the above embodiment can improve mechanical strength.

[0009] In one of the above embodiments, at least one of the pair of internal electrodes may have a first surface and a second surface that face each other in the direction in which the first inner wall surface and the second inner wall surface face each other. The first surface may be in contact with the first inner wall surface. The second surface may be exposed to the cavity and inclined with respect to the direction in which the first inner wall surface and the second inner wall surface face each other. When a transient voltage is applied to a pair of external electrodes, discharge occurs at the portions of the pair of internal electrodes that face each other and where the cavities are exposed. If the opposing area of ​​the pair of internal electrodes is small, the discharge may concentrate locally, potentially degrading the transient voltage protection characteristics. In a configuration where the second surface is inclined with respect to the direction in which the first and second internal wall surfaces face each other, the opposing area of ​​the pair of internal electrodes increases compared to a configuration where the second surface is perpendicular to the direction in which the first and second internal wall surfaces face each other. Therefore, this configuration suppresses the degradation of transient voltage protection characteristics.

[0010] In one of the above embodiments, each of the pair of internal electrodes may have a first surface and a second surface. Each second surface may face each other in the direction in which the pair of internal electrodes face each other. In a configuration where each of the pair of internal electrodes has a second surface, and each second surface faces the other in the direction in which the pair of internal electrodes face each other, the opposing surface area of ​​the pair of internal electrodes is further increased. Therefore, this configuration further suppresses the deterioration of transient voltage protection characteristics.

[0011] In one of the above embodiments, each of the pair of internal electrodes may have a side edge that is exposed to the cavity and connects the first surface and the second surface. Each side edge may face each other in the direction in which the pair of internal electrodes are facing each other. The thickness of each of the pair of internal electrodes may decrease as it approaches the side edge. In a configuration where the thickness of each of the pair of internal electrodes decreases as it approaches the side edge, the opposing area of ​​the pair of internal electrodes tends to increase. Therefore, this configuration can suppress the deterioration of transient voltage protection characteristics.

[0012] In one of the above embodiments, the body may have a discharge assist portion in contact with a pair of internal electrodes. The discharge assist portion may constitute a first inner wall surface that defines a cavity. In a configuration where the discharge assist portion constitutes the first inner wall surface defining the cavity, discharge reliably occurs between the pair of internal electrodes. Therefore, this configuration reliably improves transient voltage protection characteristics.

[0013] In one of the above embodiments, the discharge assist portion may be curved in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other. In a configuration where the discharge assist section is curved in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the opposing area of ​​the pair of internal electrodes tends to increase. Therefore, this configuration can suppress the deterioration of transient voltage protection characteristics.

[0014] In one of the above embodiments, the pair of internal electrodes may be curved along the discharge assist portion in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other. In a configuration where a pair of internal electrodes are curved along the discharge assist portion in a cross-section along the direction in which the first and second inner wall surfaces face each other, the opposing area of ​​the pair of internal electrodes tends to increase further. Therefore, this configuration can further suppress the deterioration of transient voltage protection characteristics.

[0015] In one of the above embodiments, each of the pair of internal electrodes may be exposed to the cavity and have a side edge connecting the first surface and the second surface. The second surface may include a first portion and a second portion that are exposed to the cavity. The first portion may be located closer to the side edge than the second portion. The shortest distance between the first portion and the second inner wall surface may be greater than the shortest distance between the second portion and the second inner wall surface. A configuration in which the shortest distance between the first part and the second inner wall surface is greater than the shortest distance between the second part and the second inner wall surface reliably realizes a configuration in which the second surface is inclined with respect to the direction in which the first inner wall surface and the second inner wall surface face each other.

[0016] In one such aspect, the second surface may include a first region exposed to the cavity and a second region not exposed to the cavity. The degrees of inclination with respect to the direction in which the first inner wall surface and the second inner wall surface face each other may be different between the first region and the second region.

[0017] In one such aspect, in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the second inner wall surface may be substantially linear. The configuration in which the contour of the second inner wall surface is substantially linear in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other can reliably realize a transient voltage protection device capable of improving mechanical strength.

[0018] In one such aspect, in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the second inner wall surface may protrude toward the first inner wall surface. The configuration in which the contour of the second inner wall surface protrudes toward the first inner wall surface in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other can reliably realize a transient voltage protection device capable of improving mechanical strength.

Advantages of the Invention

[0019] One aspect of the present invention provides a transient voltage protection device capable of improving mechanical strength.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a perspective view showing a transient voltage protection device according to an embodiment. <able> [Figure 2] FIG. 2 is an exploded perspective view showing the structure of the body. [Figure 3] FIG. 3 is a view showing a pair of internal electrodes and a discharge assisting portion. [Figure 4] FIG. 4 is a view showing a cross-sectional configuration along line IV-IV of FIG. 1. [Figure 5] FIG. 5 is a view showing a cross-sectional configuration along line V-V of FIG. 1. [Figure 6] Figure 6 shows a cross-sectional configuration of a transient voltage protection device according to a modified example of this embodiment. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described in detail below with reference to the attached drawings. In this description, the same reference numerals will be used for elements that are the same or have the same function, and redundant explanations will be omitted.

[0022] The configuration of the 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. Figure 2 is an exploded perspective view showing the configuration of the basic body. Figure 3 is a diagram showing a pair of internal electrodes and a discharge assist section. Figure 4 is a diagram showing the cross-sectional configuration along the line IV-IV in Figure 1. Figure 5 is a diagram showing the cross-sectional configuration along the line VV in Figure 1.

[0023] As shown in Figures 1 and 2, the transient voltage protection device 1 comprises a body 2, a pair of external electrodes 3 and 4, and a pair of internal electrodes 5 and 6. The transient voltage protection device 1 is mounted on electronic equipment not shown. The transient voltage protection device 1 protects electronic equipment from transient voltages. Electronic equipment protected by the transient voltage protection device 1 includes, for example, a circuit board or electronic components. Transient voltages are caused, for example, by electrostatic discharge (ESD).

[0024] Body 2 has a rectangular parallelepiped shape. The rectangular parallelepiped shape includes, for example, a rectangular parallelepiped shape with chamfered corners and edges, and a rectangular parallelepiped shape with rounded corners and edges. Body 2 has a pair of opposing end faces 2a, 2b, a pair of opposing side faces 2c, 2d, and a pair of opposing side faces 2e, 2f. 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 constitute the outer surface of Body 2. The four side faces 2c, 2d, 2e, 2f are adjacent to the end faces 2a and 2b, respectively, and extend in the first direction D1 to connect the end faces 2a and 2b. One of the four sides 2c, 2d, 2e, and 2f is defined as the mounting side facing the electronic device on which the transient voltage protection device 1 is mounted.

[0025] As shown in Figure 2, the base body 2 has a main body portion 20. The main body portion 20 is constructed by laminating a plurality of insulating layers 20a in a third direction D3. The main body portion 20 includes a plurality of laminated insulating layers 20a. In the main body portion 20, each insulating layer 20a is integrated to such an extent that the boundaries between each insulating layer 20a are not visible. Each insulating layer 20a is constructed, for example, as a sintered body of a ceramic green sheet containing insulating material. The main body portion 20 includes a pair of end faces 2a, 2b and four side faces 2c, 2d, 2e, 2f.

[0026] 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 insulating layer 20a may consist of a single ceramic material or of two or more types of ceramic materials. The insulating layer 20a may contain glass. The insulating layer 20a may contain copper oxide (CuO or Cu2O) to enable low-temperature sintering.

[0027] The first direction D1 is the length direction of the element 2, the second direction D2 is the width direction of the element 2, and the third direction D3 is the height direction of the element 2. The length of the element 2 is, for example, 0.6 mm or more and 2.0 mm or less. The width of the element 2 is, for example, 0.3 mm or more and 1.2 mm or less. The height of the element 2 is, for example, 0.2 mm or more and 1.2 mm or less. In this embodiment, the length of the element 2 is 1.0 mm, the width of the element 2 is 0.5 mm, and the height of the element 2 is 0.5 mm.

[0028] External electrodes 3 and 4 are positioned on the base body 2. External electrodes 3 and 4 are positioned on the base body 2 so as to face each other in the first direction D1. External electrodes 3 and 4 are positioned at both ends of the base body 2 in the first direction D1. External electrodes 3 and 4 are spaced apart from each other in the first direction D1.

[0029] The external electrode 3 is positioned on the end face 2a. The external electrode 3 is 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 parts of each of the four sides 2c, 2d, 2e, and 2f. The parts of the four sides 2c, 2d, 2e, and 2f that are covered by the external electrode 3 are located closer to the end face 2a on the corresponding side 2c, 2d, 2e, and 2f. The external electrode 3 is positioned on the entire surface of the end face 2a and on the ends of the sides 2c, 2d, 2e, and 2f that are closer to the end face 2a.

[0030] The external electrode 4 is positioned on the end face 2b. The external electrode 4 is 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 parts of each of the four sides 2c, 2d, 2e, and 2f. The parts of the four sides 2c, 2d, 2e, and 2f that are covered by the external electrode 4 are located closer to the end face 2b on the corresponding side 2c, 2d, 2e, and 2f. The external electrode 4 is positioned on the entire surface of the end face 2b and on the ends of the sides 2c, 2d, 2e, and 2f that are closer to the end face 2b.

[0031] The internal electrodes 5 and 6 are arranged within the substrate 2 so as to face each other in the second direction D2. Each internal electrode 5 and 6 extends in the first direction D1. Internal electrode 5 is positioned closer to side surface 2e. Internal electrode 6 is positioned closer to side surface 2f. In the third direction D3, internal electrodes 5 and 6 are positioned at the same height, i.e., at the same stacking position. As shown in Figure 2, internal electrodes 5 and 6 are positioned on the same insulating layer 20a. Internal electrodes 5 and 6 are positioned approximately in the center of the stacking direction of the insulating layer 20a in the third direction D3.

[0032] As shown in Figure 3, the internal electrode 5 has a pair of ends 5a, 5b, a pair of opposing side edges 5c, 5d, and a pair of opposing surfaces 5e, 5f. Side edge 5c faces the internal electrode 6. Each side edge 5c, 5d may constitute a surface. Each side edge 5c, 5d is adjacent to surface 5e and surface 5f, respectively. The internal electrode 5 is spaced apart from the end surface 2b and the sides 2c, 2d, 2e, 2f. For example, if surface 5e constitutes the first surface, then surface 5f constitutes the second surface.

[0033] End 5a is exposed to the end face 2a. End 5a is connected to the external electrode 3. In this embodiment, end 5a is directly connected to the external electrode 3. End 5a constitutes a connecting end that is connected to the external electrode 3. End 5a may constitute a tip face. End 5b is located on the opposite side of end 5a in the first direction D1. End 5b is located inside the base body 2 and is not exposed to the outer surface of the base body 2. End 5b is spaced apart from each end face 2a, 2b. In this embodiment, end 5b includes not only the tip of the internal electrode 5 but also a region from the tip of the internal electrode 5 up to a predetermined length. Therefore, end 5b has the predetermined length in the first direction D1. End 5b is embedded in the base body 2 and is in contact only with the base body 2. Viewed from the third direction D3, end 5b is spaced apart from the external electrode 4 and does not overlap with the external electrode 4. End 5b may consist only of the tip of the internal electrode 5. In this case, end 5b may consist only of the tip surface.

[0034] As shown in Figure 3, the internal electrode 6 has a pair of ends 6a, 6b, a pair of opposing side edges 6c, 6d, and a pair of opposing surfaces 6e, 6f. The side edge 6c faces the internal electrode 5. Each side edge 6c, 6d may constitute a surface. Each side edge 6c, 6d is adjacent to surface 6e and surface 6f, respectively. The internal electrode 6 is spaced apart from the end face 2a and the side surfaces 2c, 2d, 2e, 2f. For example, if surface 6e constitutes the first surface, then surface 6f constitutes the second surface.

[0035] End 6a is exposed to the end face 2b. End 6a is connected to the external electrode 4. In this embodiment, end 6a is directly connected to the external electrode 4. End 6a constitutes a connecting end connected to the external electrode 4. End 6a may constitute a tip face. End 6b is located on the opposite side of end 6a in the first direction D1. End 6b is located inside the base body 2 and is not exposed to the outer surface of the base body 2. End 6b is spaced apart from each end face 2a, 2b. In this embodiment, end 6b includes not only the tip of the internal electrode 6 but also a region from the tip of the internal electrode 6 to a predetermined length. Therefore, end 6b has the predetermined length in the first direction D1. End 6b is embedded in the base body 2 and is in contact only with the base body 2. Viewed from the third direction D3, end 6b is spaced apart from the external electrode 3 and does not overlap with the external electrode 3. End 6b may consist only of the tip of the internal electrode 6. In this case, end 6b may consist only of the tip surface.

[0036] 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 also 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 contain different conductive materials.

[0037] External electrodes 3 and 4 are formed, for example, by baking a conductive paste applied to the outer surface of the base body 2. The conductive paste for forming the external electrodes 3 and 4 includes the conductive material described above. Internal electrodes 5 and 6 are formed, for example, by baking a conductive paste applied to an insulating green sheet together with the insulating green sheet. The conductive paste is applied to the insulating green sheet, for example, by printing. The conductive paste for forming the internal electrodes 5 and 6 also includes the conductive material described above.

[0038] As shown in Figures 2 to 5, the base body 2 has a discharge assist section 21. The discharge assist section 21 is located inside the base body 2. The discharge assist section 21 is located inside the base body 2 so as to be continuous with the main body 20. The discharge assist section 21 has a rectangular shape when viewed from a third direction D3. The discharge assist section 21 includes a pair of long sides extending in a first direction D1 and a pair of short sides extending in a second direction D2. The planar shape of the discharge assist section 21 shows the shape when viewed from a third direction D3. The rectangular shape includes shapes with rounded corners and shapes with rounded corners. The discharge assist section 21 is spaced apart from the outer surface of the base body 2. The discharge assist section 21 is not exposed from the base body 2.

[0039] The length of the discharge assist portion 21 is, for example, 0.03 mm or more and 1.6 mm or less. The width of the discharge assist portion 21 is, for example, 0.03 mm or more and 0.9 mm or less. The thickness of the discharge assist portion 21 is, for example, 0.5 μm or more and 10 μm or less. In this embodiment, the length, width, and thickness of the discharge assist portion 21 are 0.5 mm, 0.2 mm, and 2 μm, respectively. The length, width, and thickness of the discharge assist portion 21 are defined, for example, by the length in the first direction D1, the length in the second direction D2, and the length in the third direction D3, respectively.

[0040] The discharge assist section 21 includes a pair of surfaces 21a and 21b that face each other in the third direction D3. Surface 21a is in contact with the internal electrodes 5 and 6. The internal electrodes 5 and 6 are arranged on surface 21a. Surface 21a includes a portion covered by the internal electrodes 5 and 6 and a portion exposed from the internal electrodes 5 and 6. Surface 21b is continuous with the main body 20. The discharge assist section 21 is in contact with the internal electrodes 5 and 6 and also connects the internal electrodes 5 and 6 to each other. The internal electrodes 5 and 6 are connected to each other via the discharge assist section 21. Together with the internal electrodes 5 and 6, the discharge assist section 21 constitutes a transient voltage suppressor. The transient voltage suppressor has transient voltage absorption performance.

[0041] In this embodiment, one end of the discharge assist portion 21 in the first direction D1 is located inside the base body 2 beyond the end 5b of the internal electrode 5 in the first direction D1. The other end of the discharge assist portion 21 in the first direction D1 is located inside the base body 2 beyond the end 6b of the internal electrode 6 in the first direction D1. Viewed from the third direction D3, one end of the discharge assist portion 21 in the second direction D2 coincides with the side edge 5d of the internal electrode 5. Viewed from the third direction D3, the other end of the discharge assist portion 21 in the second direction D2 coincides with the side edge 6d of the internal electrode 6.

[0042] The discharge assist unit 21 includes an insulator and metal particles. The insulator is, for example, made of 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 assist unit 21 may contain only one type of ceramic material selected from this group, or it may contain two or more types of 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 assist unit 21 may also contain semiconductor particles. The semiconductor particles are, for example, made of RuO2. The discharge assist unit 21 may also contain glass.

[0043] The discharge assist unit 21 is formed, for example, by firing a slurry applied to an insulating green sheet together with the insulating green sheet. The slurry contains the above-mentioned ceramic material and metal particles. The slurry is applied to the insulating green sheet, for example, by printing.

[0044] As shown in Figures 3 and 4, a cavity S is formed inside the base body 2. The cavity S is spaced apart from the outer surface of the base body 2. The surfaces defining the cavity S include the side edge 5c and surface 5f of the internal electrode 5, and the side edge 6c and surface 6f of the internal electrode 6. The main body 20 includes an inner wall surface 20b that defines the cavity S and faces surface 21a in a third direction D3, and a pair of inner wall surfaces 20c that define the cavity S and face each other in a second direction D2. The surfaces defining the cavity S include the inner wall surface 20b, the pair of inner wall surfaces 20c, and the surface 21a of the discharge assist section 21. For example, if surface 21a constitutes the first inner wall surface that defines the cavity S, then inner wall surface 20b constitutes the second inner wall surface that defines the cavity S.

[0045] As shown in Figure 4, in the cross section along the third direction D3, the contour of surface 21a and the contour of inner wall surface 20b exhibit different shapes. The cross section along the third direction D3 is, as shown in Figure 4, for example, a cross section obtained by cutting the base body 2 with a plane perpendicular to the first direction D1 at the location where the cavity S is formed. The contour of surface 21a exhibits a curved shape. The contour of inner wall surface 20b exhibits a substantially straight shape. The contour of inner wall surface 20b exhibits a substantially straight shape along the second direction D2. In this embodiment, the contours of the pair of inner wall surfaces 20c exhibit a shape inclined with respect to the third direction D3. The contours of the pair of inner wall surfaces 20c may also exhibit a substantially straight shape along the third direction D3. The cross section along the third direction D3 may also be a cross section obtained by cutting the base body 2 with a plane perpendicular to the second direction D2 at the location where the cavity S is formed.

[0046] Viewed from the third direction D3, the cavity S is located inside the outer edge of the discharge assist portion 21. The cavity S is shorter than the discharge assist portion 21 in both the first direction D1 and the second direction D2. Viewed from the third direction D3, one end of the cavity S in the second direction D2 is located inside the side edge 5d of the internal electrode 5. Viewed from the third direction D3, the other end of the cavity S in the second direction D2 is located inside the side edge 6d of the internal electrode 6.

[0047] The cavity S is formed, for example, by firing an organic lacquer applied to an insulating green sheet together with the insulating green sheet. The cavity S is formed by the burning away of the organic lacquer. The organic lacquer contains an organic solvent and an organic binder. The organic lacquer is applied to the insulating green sheet, for example, by printing.

[0048] As shown in Figure 4, the discharge assist section 21 is curved in a cross-section along the third direction D3. The discharge assist section 21 is curved to form an arc shape in a cross-section along the third direction D3. Surfaces 21a and 21b are curved to form an arc shape. In this embodiment, surfaces 21a and 21b are curved such that both ends of the discharge assist section 21 taper in the second direction D2. The internal electrodes 5 and 6 are also curved in a cross-section along the third direction D3. The internal electrodes 5 and 6 are curved to follow the discharge assist section 21. The internal electrodes 5 and 6 are also curved to form an arc shape in a cross-section along the third direction D3, similar to the discharge assist section 21. In this embodiment, surface 5e of the internal electrode 5 and surface 6e of the internal electrode 6 are curved to form an arc shape along surface 21a of the discharge assist section 21.

[0049] As shown in Figure 4, the surface 5f of the internal electrode 5 and the surface 6f of the internal electrode 6 are inclined with respect to the third direction D3. Surfaces 5f and 6f are inclined in the direction from the inner wall surface 20b toward surface 21a within the third direction D3. As described above, since surfaces 5f and 6f are inclined with respect to the third direction D3, surfaces 5f and 6f face each other in the second direction D2. Within the cavity S, the side edges 5c and 6c and surfaces 5f and 6f each face each other in the second direction D2.

[0050] The thickness of the internal electrode 5 decreases as it approaches the side edge 5c. The thickness of the internal electrode 5 is defined by the length of the internal electrode 5 in the third direction D3. In this embodiment, the thickness of the internal electrode 5 decreases from approximately the center in the second direction D2 to the side edge 5c. The thickness of the internal electrode 5 is minimum at the side edge 5c. The thickness of the internal electrode 5 may decrease continuously as it approaches the side edge 5c, or it may decrease in steps.

[0051] The thickness of the internal electrode 6 decreases as it approaches the side edge 6c. The thickness of the internal electrode 6 is defined by the length of the internal electrode 6 in the third direction D3. In this embodiment, the thickness of the internal electrode 6 decreases from approximately the center in the second direction D2 to the side edge 6c. The thickness of the internal electrode 6 is minimum at the side edge 6c. The thickness of the internal electrode 6 may decrease continuously as it approaches the side edge 6c, or it may decrease in steps. The thickness of the internal electrodes 5 and 6 may be measured, for example, based on a cross-section obtained by cutting the base body 2 with a plane perpendicular to the first direction D1 at a position including the internal electrodes 5 and 6.

[0052] As shown in Figure 4, surface 5f includes a region 51 exposed to the cavity S. Surface 5f further includes portions 51a and 51b exposed to the cavity S. Region 51 includes portions 51a and 51b. In this embodiment, region 51 is composed of portion 51a and portion 51b. In the second direction D2, portion 51a is located closer to the side edge 5c than portion 51b. For example, if portion 51a constitutes the first portion, then portion 51b constitutes the second portion.

[0053] As described above, the contour of the inner wall surface 20b is substantially straight along the second direction D2, and the surface 5f is inclined with respect to the third direction D3. The shortest distance d1 between portion 51a and the inner wall surface 20b and the shortest distance d2 between portion 51b and the inner wall surface 20b are different from each other. In this embodiment, the shortest distance d1 is greater than the shortest distance d2. The shortest distance d1 is defined by the distance between portion 51a and the inner wall surface 20b in the third direction D3, and the shortest distance d2 is defined by the distance between portion 51b and the inner wall surface 20b in the third direction D3.

[0054] Surface 6f includes a region 61 exposed to the cavity S. Surface 6f further includes portions 61a and 61b exposed to the cavity S. Region 61 includes portions 61a and 61b. In this embodiment, region 61 is composed of portion 61a and portion 61b. In the second direction D2, portion 61a is located closer to the side edge 6c than portion 61b. For example, if portion 61a constitutes the first portion, then portion 61b constitutes the second portion.

[0055] As described above, the contour of the inner wall surface 20b is substantially straight along the second direction D2, and the surface 6f is inclined with respect to the third direction D3. The shortest distance d3 between portion 61a and the inner wall surface 20b and the shortest distance d4 between portion 61b and the inner wall surface 20b are different from each other. In this embodiment, the shortest distance d3 is greater than the shortest distance d4. The shortest distance d3 is defined by the distance between portion 61a and the inner wall surface 20b in the third direction D3, and the shortest distance d4 is defined by the distance between portion 61b and the inner wall surface 20b in the third direction D3.

[0056] The shortest distance d1 is, for example, 3 μm or more and 40 μm or less. The shortest distance d2 is, for example, 1 μm or more and 30 μm or less. In this embodiment, the shortest distance d1 is 15 μm and the shortest distance d2 is 10 μm. The shortest distance d3 is, for example, 3 μm or more and 40 μm or less. The shortest distance d4 is, for example, 1 μm or more and 30 μm or less. In this embodiment, the shortest distance d3 is 15 μm and the shortest distance d4 is 10 μm.

[0057] As shown in Figure 5, surface 5f includes a region 52 that is not exposed to the cavity S. In this embodiment, surface 5f consists of a region 51 exposed to the cavity S and a region 52 not exposed to the cavity S. Region 52 is in contact only with the base body 2. The entire region 52 is covered by the base body 2. As shown in Figures 4 and 5, the degree of inclination with respect to the third direction D3 differs between region 51 and region 52. The degree of inclination with respect to the third direction D3 in region 52 is smaller than the degree of inclination with respect to the third direction D3 in region 51. In this embodiment, the degree of inclination with respect to the third direction D3 is defined by the angle of inclination with respect to the third direction D3. The angles of inclination with respect to the third direction D3 differ between region 51 and region 52. The angle of inclination with respect to the third direction D3 in region 52 is smaller than the angle of inclination with respect to the third direction D3 in region 51. In this embodiment, the angle of inclination with respect to the third direction D3 in region 52 is approximately a right angle. The angle of inclination with respect to the third direction D3 in regions 51 and 52 may be measured based on a cross-section obtained by cutting the element 2 with a plane perpendicular to the first direction D1 at a position including regions 51 and 52. For example, if region 51 constitutes the first region, then region 52 constitutes the second region.

[0058] Surface 6f includes a region 62 that is not exposed to the cavity S. In this embodiment, surface 6f is composed of a region 61 that is exposed to the cavity S and a region 62 that is not exposed to the cavity S. Region 62 is in contact only with the base body 2. The entire region 62 is covered by the base body 2. The degree of inclination with respect to the third direction D3 is different between region 61 and region 62. The degree of inclination with respect to the third direction D3 in region 62 is smaller than the degree of inclination with respect to the third direction D3 in region 61. The angle of inclination with respect to the third direction D3 is different between region 61 and region 62. The angle of inclination with respect to the third direction D3 in region 62 is smaller than the angle of inclination with respect to the third direction D3 in region 61. In this embodiment, the angle of inclination with respect to the third direction D3 in region 62 is approximately a right angle. The angle of inclination with respect to the third direction D3 in regions 61 and 62 may be measured, for example, based on a cross-section obtained by cutting the element 2 with a plane perpendicular to the first direction D1 at a position including regions 61 and 62. For example, if region 61 constitutes the first region, then region 62 constitutes the second region.

[0059] As explained above, in the transient voltage protection device 1, the contour of surface 21a and the contour of inner wall surface 20b exhibit different shapes in a cross-section along the third direction D3. Compared to a configuration in which the contour of surface 21a and the contour of inner wall surface 20b exhibit the same shape, the transient voltage protection device 1 tends to have a smaller cavity volume S. The volume of cavity S is related to the mechanical strength of the transient voltage protection device 1. When the volume of cavity S is small, the mechanical strength of the transient voltage protection device tends to improve. Therefore, the transient voltage protection device 1 can have improved mechanical strength.

[0060] In the transient voltage protection device 1, at least one of the surfaces 5f and 6f is exposed to the cavity S and is inclined with respect to the third direction D3. When a transient voltage is applied to a pair of external electrodes 3 and 4, discharge occurs at the portions of a pair of internal electrodes 5 and 6 that face each other and are exposed to the cavity S. If the opposing area of ​​the pair of internal electrodes 5 and 6 is small, the discharge may concentrate locally, potentially degrading the transient voltage protection characteristics. In a transient voltage protection device 1 where at least one of surfaces 5f and 6f is exposed to the cavity S and inclined with respect to the third direction D3, the opposing area of ​​the pair of internal electrodes 5 and 6 increases compared to a configuration where surface 5f or surface 6f is perpendicular to the third direction D3. Therefore, the transient voltage protection device 1 suppresses the degradation of transient voltage protection characteristics.

[0061] In the transient voltage protection device 1, surfaces 5f and 6f are exposed to the cavity S and are inclined with respect to the third direction D3. In transient voltage protection device 1, the opposing area of ​​the pair of internal electrodes 5 and 6 is further increased. Therefore, transient voltage protection device 1 further suppresses the degradation of transient voltage protection characteristics.

[0062] In the transient voltage protection device 1, the internal electrode 5 is exposed to the cavity S and has a side edge 5c connecting surfaces 5e and 5f. The internal electrode 6 is exposed to the cavity S and has a side edge 6c connecting surfaces 6e and 6f. The side edges 5c and 6c face each other in the second direction D2. The thickness of the internal electrode 5 decreases as it approaches the side edge 5c. The thickness of the internal electrode 6 decreases as it approaches the side edge 6c. In transient voltage protection device 1, the opposing area of ​​the pair of internal electrodes 5 and 6 tends to increase. Therefore, transient voltage protection device 1 can suppress the deterioration of transient voltage protection characteristics.

[0063] In the transient voltage protection device 1, the element 2 has a discharge assist portion 21 that is in contact with a pair of internal electrodes 5 and 6. The discharge assist portion 21 constitutes an inner wall surface that defines the cavity S. In transient voltage protection device 1, discharge reliably occurs between the pair of internal electrodes. Therefore, transient voltage protection device 1 reliably improves transient voltage protection characteristics.

[0064] In the transient voltage protection device 1, the discharge assist section 21 is curved in cross-section along the third direction D3. In transient voltage protection device 1, the opposing area of ​​the pair of internal electrodes 5 and 6 tends to increase. Therefore, transient voltage protection device 1 can suppress the deterioration of transient voltage protection characteristics.

[0065] In the transient voltage protection device 1, the pair of internal electrodes 5 and 6 are curved in a cross-section along the third direction D3 so as to follow the discharge assist portion 21. In transient voltage protection device 1, the opposing area of ​​the pair of internal electrodes 5 and 6 is more easily increased. Therefore, transient voltage protection device 1 can further suppress the deterioration of transient voltage protection characteristics.

[0066] In transient voltage protection device 1, the shortest distance d1 between portion 51a and the inner wall surface 20b is greater than the shortest distance d2 between portion 51b and the inner wall surface 20b. The shortest distance d3 between portion 61a and the inner wall surface 20b is greater than the shortest distance d4 between portion 61b and the inner wall surface 20b. The transient voltage protection device 1 reliably realizes a configuration in which surfaces 5f and 6f are inclined with respect to the third direction D3.

[0067] In transient voltage protection device 1, the degree of inclination with respect to the third direction D3 is different in region 51 and region 52. The degree of inclination with respect to the third direction D3 is different in region 61 and region 62. In transient voltage protection device 1, the degree of inclination with respect to the third direction D3 in regions 51 and 61 may increase. In this case, the opposing area of ​​the pair of internal electrodes 5 and 6 tends to increase. Therefore, transient voltage protection device 1 can suppress the deterioration of transient voltage protection characteristics.

[0068] In the transient voltage protection device 1, the contour of the inner wall surface 20b is substantially straight in a cross-section along the third direction D3. The transient voltage protection device 1 reliably realizes a transient voltage protection device that can improve mechanical strength.

[0069] In transient voltage protection device 1, the degree of inclination with respect to the third direction D3 in region 52 is less than the degree of inclination with respect to the third direction D3 in region 51. The degree of inclination with respect to the third direction D3 in region 62 is less than the degree of inclination with respect to the third direction D3 in region 61. In the transient voltage protection device 1, regions 52 and 62 and the element 2 are in reliable contact, improving the strength of the element 2. Therefore, the transient voltage protection device 1 can improve its mechanical strength.

[0070] Next, with reference to Figure 6, the configuration of a modified example of the transient voltage protection device 1 will be described. Figure 6 is a diagram showing the cross-sectional configuration of the transient voltage protection device according to the modified example of this embodiment. In this modified example, the configuration of the inner wall surface 20b differs from that of the embodiment described above. The differences between the embodiment described above and this modified example will be mainly described below. Figure 6 shows the cross-sectional configuration of the transient voltage protection device 1 (base body 2) according to this modified example when it is cut at a position corresponding to the cutting position in Figure 4.

[0071] In the cross-section along the third direction D3, the contour of the inner wall surface 20b protrudes toward the surface 21a. In this modified example, the central portion of the contour of the inner wall surface 20b in the second direction D2 protrudes toward the surface 21a. The position of the contour of the inner wall surface 20b that protrudes toward the surface 21a is not limited to the position described above. The portion of the contour of the inner wall surface 20b located closer to the internal electrode 5 may protrude toward the surface 21a, and the portion located closer to the internal electrode 6 may protrude toward the surface 21a. In this modified example as well, the cross-section along the third direction D3 is, as shown in Figure 6, a cross-section obtained by cutting the base body 2 with a plane perpendicular to the first direction D1 at the position where the cavity S is formed.

[0072] While embodiments of the present invention have been described above, the present invention is not necessarily limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0073] Neither surface 5f nor surface 6f is necessarily inclined with respect to the third direction D3. In this case, at least one of surfaces 5f and 6f may be inclined with respect to the third direction D3. Alternatively, neither surface 5f nor surface 6f may be perpendicular to the third direction D3. As described above, the transient voltage protection device 1 in which both surfaces 5f and 6f are inclined with respect to the third direction D3 further suppresses the deterioration of transient voltage protection characteristics.

[0074] In transient voltage protection device 1, the thickness of the internal electrode 5 does not necessarily decrease as it approaches the side edge 5c. The thickness of the internal electrode 6 does not necessarily decrease as it approaches the side edge 6c. A transient voltage protection device 1 in which the thickness of the internal electrode 5 decreases as it approaches the side edge 5c and the thickness of the internal electrode 6 decreases as it approaches the side edge 6c can suppress the deterioration of transient voltage protection characteristics as described above.

[0075] In transient voltage protection device 1, the element 2 does not necessarily have to have a discharge assist section 21. Transient voltage protection device 1 in which the element 2 has a discharge assist section 21 reliably improves transient voltage protection characteristics as described above. In a configuration in which the element 2 does not have a discharge assist section 21, the main body 20 includes another inner wall surface that faces the inner wall surface 20b in a third direction D3. In this case, the other inner wall surface together with the inner wall surface 20b and the pair of inner wall surfaces 20c define a cavity S.

[0076] In transient voltage protection device 1, the discharge assist portion 21 does not need to be curved in cross-section along the third direction D3. Transient voltage protection device 1 in which the discharge assist portion 21 is curved in cross-section along the third direction D3 can suppress the deterioration of transient voltage protection characteristics as described above.

[0077] In the transient voltage protection device 1, the pair of internal electrodes 5 and 6 do not necessarily have to be curved along the discharge assist portion 21 in a cross-section along the third direction D3. A transient voltage protection device 1 in which the pair of internal electrodes 5 and 6 are curved along the discharge assist portion 21 in a cross-section along the third direction D3 can further suppress the deterioration of transient voltage protection characteristics, as described above.

[0078] In transient voltage protection device 1, the shortest distance d1 between portion 51a and inner wall surface 20b does not have to be greater than the shortest distance d2 between portion 51b and inner wall surface 20b. The shortest distance d3 between portion 61a and inner wall surface 20b does not have to be greater than the shortest distance d4 between portion 61b and inner wall surface 20b. Transient voltage protection device 1 in which the shortest distance d1 is greater than the shortest distance d2 and the shortest distance d3 is greater than the shortest distance d4 reliably realizes a configuration in which surfaces 5f and 6f are inclined with respect to the third direction D3, as described above.

[0079] In transient voltage protection device 1, the degree of inclination with respect to the third direction D3 does not have to be different in region 51 and region 52. The degree of inclination with respect to the third direction D3 does not have to be different in region 61 and region 62. Transient voltage protection device 1 in which the degree of inclination with respect to the third direction D3 is different in region 51 and region 52, and the degree of inclination with respect to the third direction D3 is different in region 61 and region 62, can suppress the deterioration of transient voltage protection characteristics as described above.

[0080] In transient voltage protection device 1, the contour of the inner wall surface 20b does not have to be substantially straight in a cross-section along the third direction D3. Transient voltage protection device 1 in which the contour of the inner wall surface 20b is substantially straight in a cross-section along the third direction D3 reliably realizes a transient voltage protection device that can improve mechanical strength, as described above.

[0081] As can be seen from the above-described embodiments and modifications, this specification includes the following embodiments. (Note 1) A base body with a hollow space formed inside, A pair of external electrodes arranged on the aforementioned body, The system comprises a pair of internal electrodes, which are arranged within the body so as to face each other and are connected to corresponding external electrodes of the pair of external electrodes, The aforementioned body has a first inner wall surface and a second inner wall surface that define the cavity and are opposite to each other. The pair of internal electrodes are exposed to the cavity and are positioned on the first inner wall surface. A transient voltage protection device in which, in a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the first inner wall surface and the contour of the second inner wall surface exhibit different shapes from each other. (Note 2) At least one of the pair of internal electrodes has a first surface and a second surface that face each other in the direction in which the first inner wall surface and the second inner wall surface face each other. The first surface is in contact with the first inner wall surface. The transient voltage protection device as described in Appendix 1, wherein the second surface is exposed to the cavity and is inclined with respect to the direction in which the first inner wall surface and the second inner wall surface face each other. (Note 3) Each of the pair of internal electrodes has the first surface and the second surface, Each of the aforementioned second surfaces faces each other in the direction in which the pair of internal electrodes face each other, in the transient voltage protection device as described in Appendix 2. (Note 4) Each of the pair of internal electrodes has a side edge that is exposed to the cavity and connects the first surface and the second surface. Each of the aforementioned side edges faces each other in the direction in which the pair of internal electrodes are facing each other. The transient voltage protection device according to claim 2, wherein the thickness of each of the pair of internal electrodes decreases as it approaches the side edge. (Note 5) The aforementioned body has a discharge assist portion that is in contact with the pair of internal electrodes, The discharge assist portion constitutes the first inner wall surface defining the cavity, and is a transient voltage protection device as described in any one of the appendices 1 to 4. (Note 6) The transient voltage protection device described in Appendix 5, wherein the discharge assist portion is curved in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other. (Note 7) The transient voltage protection device according to Appendix 6, wherein the pair of internal electrodes are curved along the discharge assist portion in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other. (Note 8) Each of the pair of internal electrodes has a side edge that is exposed to the cavity and connects the first surface and the second surface. The second surface includes the first and second portions exposed to the cavity, The first portion is located closer to the side edge than the second portion, A transient voltage protection device as described in any one of the appendices 2 to 7, wherein the shortest distance between the first portion and the second inner wall surface is greater than the shortest distance between the second portion and the second inner wall surface. (Note 9) The second surface mentioned above is, The first region exposed in the cavity, A second region not exposed to the cavity, A transient voltage protection device as described in any one of the appendices 2 to 8, wherein the degree of inclination of the first inner wall surface and the second inner wall surface with respect to the direction in which they face each other is different in the first region and the second region. (Note 10) A transient voltage protection device according to any one of the appendices 1 to 9, wherein in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the second inner wall surface is substantially straight. (Note 11) A transient voltage protection device according to any one of the appendices 1 to 9, wherein in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the second inner wall surface protrudes toward the first inner wall surface. [Explanation of symbols]

[0082] 1...Transient voltage protection device, 2...Element body, 3,4...External electrode, 5,6...Internal electrode, 5c,6c...Side edge, 5e,5f,6e,6f...Surface, 20b...Inner wall surface, 21 ...discharge auxiliary part, 21a...plane, 51,52,61,62...area, 51a,51b,61a,61b...part, d1,d2,d3,d4...shortest distance, S...cavity.

Claims

1. A base body with a hollow space formed inside, A pair of external electrodes arranged on the aforementioned body, The system comprises a pair of internal electrodes, which are arranged within the body so as to face each other and are connected to corresponding external electrodes of the pair of external electrodes, The aforementioned body has a first inner wall surface and a second inner wall surface that define the cavity and are opposite to each other. The pair of internal electrodes are exposed to the cavity and are positioned on the first inner wall surface. In a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the first inner wall surface and the contour of the second inner wall surface exhibit different shapes from each other. Each of the pair of internal electrodes has a first and second surface facing each other in the direction in which the first inner wall surface and the second inner wall surface face each other, and a side edge that is exposed to the cavity and connects the first surface and the second surface. The first surface is in contact with the first inner wall surface. The second surface is exposed to the cavity and is inclined with respect to the direction in which the first inner wall surface and the second inner wall surface face each other. Each of the aforementioned side edges faces each other in the direction in which the pair of internal electrodes are facing each other. A transient voltage protection device in which the thickness of each of the pair of internal electrodes decreases as it approaches the side edge.

2. The transient voltage protection device according to claim 1, wherein each of the second surfaces faces each other in the direction in which the pair of internal electrodes face each other.

3. The second surface includes the first and second portions exposed to the cavity, The first portion is located closer to the side edge than the second portion, The transient voltage protection device according to claim 1, wherein the shortest distance between the first portion and the second inner wall surface is greater than the shortest distance between the second portion and the second inner wall surface.

4. The second surface mentioned above is, The first region exposed in the cavity, A second region not exposed to the cavity, The transient voltage protection device according to claim 1, wherein the degree of inclination of the first inner wall surface and the second inner wall surface with respect to the direction in which they face each other is different in the first region and the second region.

5. A base body with a hollow space formed inside, A pair of external electrodes arranged on the aforementioned body, The system comprises a pair of internal electrodes, which are arranged within the body so as to face each other and are connected to corresponding external electrodes of the pair of external electrodes, The aforementioned body has a first inner wall surface and a second inner wall surface that define the cavity and are opposite to each other. The pair of internal electrodes are exposed to the cavity and are positioned on the first inner wall surface. In a cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the first inner wall surface and the contour of the second inner wall surface exhibit different shapes from each other. At least one of the pair of internal electrodes has a first surface and a second surface that face each other in the direction in which the first inner wall surface and the second inner wall surface face each other. The first surface is in contact with the first inner wall surface. The second surface is exposed to the cavity and is inclined with respect to the direction in which the first inner wall surface and the second inner wall surface face each other. The second surface mentioned above is, The first region exposed in the cavity, A second region not exposed to the cavity, A transient voltage protection device in which the first region and the second region have different degrees of inclination with respect to the direction in which the first inner wall surface and the second inner wall surface face each other.

6. Each of the pair of internal electrodes has the first surface and the second surface, The transient voltage protection device according to claim 5, wherein each of the second surfaces faces each other in the direction in which the pair of internal electrodes face each other.

7. Each of the pair of internal electrodes has a side edge that is exposed to the cavity and connects the first surface and the second surface. The second surface includes the first and second portions exposed to the cavity, The first portion is located closer to the side edge than the second portion, The transient voltage protection device according to claim 5, wherein the shortest distance between the first portion and the second inner wall surface is greater than the shortest distance between the second portion and the second inner wall surface.

8. The aforementioned body has a discharge assist portion that is in contact with the pair of internal electrodes, The transient voltage protection device according to claim 1 or 5, wherein the discharge assist portion constitutes the first inner wall surface defining the cavity.

9. The transient voltage protection device according to claim 8, wherein the discharge assist portion is curved in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other.

10. The transient voltage protection device according to claim 9, wherein the pair of internal electrodes are curved along the discharge assist portion in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other.

11. The transient voltage protection device according to claim 1 or 5, wherein in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the second inner wall surface is substantially straight.

12. The transient voltage protection device according to claim 1 or 5, wherein in the cross-section along the direction in which the first inner wall surface and the second inner wall surface face each other, the contour of the second inner wall surface protrudes toward the first inner wall surface.

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