JP7728671B2 - Transient Voltage Protection Components - Google Patents

Description

The present invention relates to transient voltage protection components.

As shown in Patent Document 1, a transient voltage protection component is known that has a pair of opposing discharge electrodes and a discharge inducing portion adjacent to the discharge electrodes. This transient voltage protection component protects circuits from ESD (Electro-Static Discharge) and prevents damage and malfunction of electronic devices caused by ESD.

In transient voltage protection components, the higher the density of the discharge triggering section, the better the ESD resistance can be expected. For this reason, during the manufacturing process of transient voltage protection components, green chips are typically fired at high temperatures of 850°C or higher to thoroughly sinter the discharge triggering section. However, firing at high temperatures can cause the metal particles contained in the discharge triggering section to grow, which can lead to a short circuit between a pair of discharge electrodes via the discharge triggering section. On the other hand, if the green chip is sintered at a low temperature below 850°C in order to prevent short circuits, the density of the discharge triggering section cannot be ensured, resulting in a decrease in ESD resistance.

WO 2009/098944

The present invention was made in light of these circumstances, and its purpose is to provide a transient voltage protection component that has a high density of discharge inducing parts and excellent ESD resistance, even when manufactured using low-temperature firing.

In order to achieve the above object, the transient voltage protection component according to the present invention comprises:
a pair of discharge electrodes facing each other across a gap;
a discharge inducing unit adjacent to the pair of discharge electrodes,
the discharge inducing unit has a base material containing glass and a plurality of metal particles dispersed in the base material,
The glass contains SiO ₂ and ZnO.

The transient voltage protection component of the present invention has the above-mentioned characteristics, which allow the density of the discharge inducing portion to be increased even when fired at low temperatures, resulting in high ESD resistance.

The glass may contain an alkaline earth metal component and/or B ₂ O ₃ .

Preferably, the substrate of the discharge inducing section contains zirconia, a non-glass material. The inclusion of zirconia in the discharge inducing section can improve adhesion between the discharge inducing section and the insulator layer in contact with the discharge inducing section. Furthermore, the inclusion of zirconia in the discharge inducing section can improve the dispersibility of metal particles contained in the discharge inducing section, further improving ESD resistance.

Preferably, the ZnO content in the substrate is 0.05 wt% or more and 15 wt% or less, based on 100 wt% of the substrate.

Preferably, the Si/Zn ratio in the substrate is 3 or greater.

Preferably, the content of alkali metal components in the substrate is 2 wt% or less per 100 wt% of the substrate.

By having the glass of the discharge inducing section have a specified composition as described above, the density and ESD resistance of the discharge inducing section can be further improved.

FIG. 1 is a perspective view showing a transient voltage protection component according to an embodiment of the present invention. FIG. 2A is a cross-sectional view taken along line IIA-IIA shown in FIG. FIG. 2B is a cross-sectional view taken along line IIB-IIB shown in FIG. FIG. 3 is an enlarged cross-sectional view of the discharge inducing portion. FIG. 4 is a plan view of a green sheet used in the manufacturing process of a transient voltage protection component. FIG. 5 is an exploded perspective view of a green chip used in the manufacturing process of a transient voltage protection component. FIG. 6A is a cross-sectional view showing a modified example of a transient voltage protection component. FIG. 6B is a cross-sectional view showing a modified example of a transient voltage protection component.

The present invention will now be described in detail based on the embodiments shown in the drawings. As shown in FIG. 1, the transient voltage protection component 2 according to this embodiment has a base body 10 having a substantially rectangular parallelepiped (substantially hexahedral) shape and a pair of external electrodes (a first external electrode 6 and a second external electrode 8) formed on the outer surface of the base body 10.

The element body 10 has a pair of end faces 10a that are approximately perpendicular to the X axis, a pair of side faces 10b that are approximately perpendicular to the Y axis, and a pair of main faces 10c that are approximately perpendicular to the Z axis. The dimensions of the element body 10 are not particularly limited and may be appropriate depending on the application. In this embodiment, the X axis, Y axis, and Z axis are mutually perpendicular.

The first external electrode 6 covers one end face 10a and is formed to extend from this end face 10a around the side face 10b and part of the main face 10c. The second external electrode 8 covers the other end face 10a and is formed to extend from this end face 10a around the side face 10b and part of the main face 10c. The first external electrode 6 and second external electrode 8 are insulated so as not to contact each other in the X-axis direction.

Figure 2A is an X-Z cross section of the transient voltage protection component 2 taken approximately at the center in the Y-axis direction. Meanwhile, Figure 2B is an X-Y cross section of the transient voltage protection component 2 taken approximately at the center in the Z-axis direction. As shown in Figures 2A and 2B, the element body 10 has multiple insulator layers 11, a pair of discharge electrodes (first discharge electrode 16 and second discharge electrode 18), a discharge inducing portion 13, and a cavity portion 15.

The multiple insulator layers 11 are all sintered bodies with electrical insulation properties, and are stacked along the Z-axis direction. The insulator layers 11 are integrated to the extent that the boundaries between the layers are not visible. There are no particular restrictions on the thickness of the insulator layers 11 or the number of layers, and these may be determined appropriately depending on the dimensions of the element body 10.

The first discharge electrode 16 and the second discharge electrode 18 are both electrode layers having a rectangular shape in a planar view and are interposed between predetermined insulator layers 11. The thicknesses of the first discharge electrode 16 and the second discharge electrode 18 are not particularly limited, but it is preferable that the first discharge electrode 16 and the second discharge electrode 18 have approximately the same average thickness. Furthermore, the first discharge electrode 16 and the second discharge electrode 18 are both layered on the same insulator layer 11, and the distance in the Z-axis direction from the main surface 10c to the first discharge electrode 16 is approximately the same as the distance in the Z-axis direction from the main surface 10c to the second discharge electrode 18. In other words, the first discharge electrode 16 and the second discharge electrode 18 are located at approximately the same height in the Z-axis direction. However, the first discharge electrode 16 and the second discharge electrode 18 are positioned at a distance from each other so as not to come into direct contact in the X-axis direction.

The first discharge electrode 16 has a lead portion 16a and a facing portion 16b. The lead portion 16a is the end of the first discharge electrode 16 facing outward in the X-axis direction. This lead portion 16a is exposed at the end surface 10a of the element body 10 and is electrically connected to the external electrode 6. On the other hand, the facing portion 16b is the end of the first discharge electrode 16 facing inward in the X-axis direction. This facing portion 16b is located inside the cavity portion 15 and faces the facing portion 18b of the second discharge electrode 18.

The second discharge electrode 18 has a lead portion 18a and a facing portion 18b. The lead portion 18a is the end of the second discharge electrode 18 facing outward in the X-axis direction. This lead portion 18a is exposed at the end surface 10a of the element body 10 and is electrically connected to the external electrode 8. On the other hand, the facing portion 18b is the end of the second discharge electrode 18 facing inward in the X-axis direction. This facing portion 18b is located inside the cavity 15 and faces the facing portion 16b of the first discharge electrode 16.

Facing portion 16b and facing portion 18b are spaced apart in the X-axis direction, forming a gap G between facing portion 16b and facing portion 18b. When a voltage equal to or greater than a predetermined value is applied between external electrode 6 and external electrode 8, a discharge occurs in gap G. The transient voltage protection component 2 prevents transient voltages from being applied to the protected object (DUP: Device Under Protection) due to the discharge between facing portion 16b and facing portion 18b. The width of gap G in the X-axis direction is not particularly limited and can be determined appropriately to achieve the desired discharge characteristics.

The discharge inducing section 13 is layered below the discharge electrodes 16, 18 in the Z-axis direction so as to contact both discharge electrodes 16, 18 in the stacking direction. In other words, the discharge inducing section 13 is formed across the first discharge electrode 16 and the second discharge electrode 18, connecting the opposing section 16b and the opposing section 18b. The discharge inducing section 13 has a substantially rectangular planar shape when viewed in the stacking direction. The width of the discharge inducing section 13 in the X-axis direction is preferably greater than the width of the gap G, and the width of the discharge inducing section 13 in the Y-axis direction is preferably greater than the width of the opposing section 16b and the width of the opposing section 18b in the Y-axis direction. The average thickness of the discharge inducing section 13 is not particularly limited, but is preferably 1 μm to 15 μm, for example. This discharge inducing section 13 has the function of facilitating the generation of a discharge between the first discharge electrode 16 and the second discharge electrode 18.

The cavity 15 is a space formed by removing organic components (lacquer) during the manufacturing process of the transient voltage protection component 2. As shown in FIG. 2A, the surfaces defining the cavity 15 include the surface near the opposing portion 16b of the first discharge electrode 16, the surface near the opposing portion 18b of the second discharge electrode 18, the surface of the discharge inducing portion 13, and the underside of the insulator layer 11 located above the discharge electrodes 16 and 18. While the shape and dimensions of the cavity 15 are not particularly limited, it is preferable that the cavity 15 be formed so as to cover the discharge inducing portion 13 when viewed from the stacking direction. This cavity 15 functions to absorb thermal expansion of the first discharge electrode 16, the second discharge electrode 18, the insulator layer 11 adjacent to the discharge electrodes, and the discharge inducing portion 13 during discharge.

Next, we will explain the materials used for each component.

The insulator layer 11 contains _one or more inorganic compounds selected from _Fe2O3 , NiO, copper oxide (CuO, _Cu2O ) _, ZnO, MgO, _SiO2 , _TiO2 , _MnCO3 , _SrCO3 , _CaCO3 , _BaCO3 , _Al2O3 , _ZrO2 , and _{B2O3 .} It is particularly preferable that the insulator layer 11 contains _ZrO2 and/or copper oxide. When two or more inorganic compounds are contained, the inorganic compounds may exist as a composite compound (e.g., _CaZrO3 ). In addition to the inorganic compounds, the insulator layer 11 may also contain glass or a minor component compound containing a rare earth element or the like.

The first discharge electrode 16 and the second discharge electrode 18 both contain a conductive material. Examples of conductive materials include Ag, Pd, Au, Pt, Cu, Ni, Al, Mo, W, and alloys containing at least one of these metal elements. The first discharge electrode 16 and the second discharge electrode 18 may contain different types of conductive materials, but it is preferable that the first discharge electrode 16 and the second discharge electrode 18 are made of the same type of conductive material. The first discharge electrode 16 and the second discharge electrode 18 may also contain trace amounts (e.g., 1 wt % or less) of non-metallic components such as S and P, and may also contain inorganic compounds contained in the insulator layer 11 as co-materials.

As shown in FIG. 3, the discharge inducing unit 13 has a substrate 31 and a plurality of metal particles 33 dispersed in the substrate 31.

The metal particles 33 have a melting point (solidus temperature) higher than the firing temperature of the element body 10. Specifically, the metal particles 33 may be Ag particles, Pd particles, Au particles, Pt particles, Cu particles, Ag-Pd alloy particles, Ag-Au alloy particles, or Ag-Pt alloy particles, with Pd particles or Ag-Pd alloy particles being preferred. The average particle size (D50) of the metal particles 33 in the cross section of the discharge inducing section 13 is preferably 2.0 μm or less. Furthermore, the content of the metal particles 33 is preferably 10 to 50 vol% relative to 100 vol% of the discharge inducing section.

The average particle size and content of the metal particles 33 can be measured by observing a cross section of the discharge inducing section 13 as shown in FIG. 3 using a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM), and then performing image analysis on the obtained cross-sectional photograph. For example, the average particle size of the metal particles 33 can be calculated by measuring the circle-equivalent diameters of at least 20 metal particles 33. The content of the metal particles 33 can be calculated based on the area ratio expressed as "total area of the metal particles 33 included in the analysis field of view/area of the analysis field of view." In this case, it is preferable to change the analysis field of view and measure the area of the metal particles 33 in an analysis field of view of at least 400 ^μm2 or more.

The substrate 31 contains glass 31a, and may also contain semiconductor compounds such as _SnO2 and _RuO2 , dielectric compounds, inorganic compounds that form the insulator layer 11, and other inorganic materials such as amorphous silica.

Glass 31a is interposed between metal particles 33, bonding them together. By being interposed between the particles, glass 31a ensures insulation between metal particles 33 and contributes to ensuring the density of the discharge inducing section 13. The content of glass 31a is preferably 10 wt% or more, and more preferably 12 wt% or more, relative to 100 wt% of the base material of the discharge inducing section 13. There is no particular upper limit to the content of glass 31a, and it can be 100 wt%, but it is preferably 50 wt% or less.

The glass 31a contains at least SiO ₂ and ZnO as major components. The ZnO content in the base material 31 is preferably 0.05 wt % or more and 15 wt % or less, and more preferably 0.10 wt % or more and 5 wt % or less, relative to 100 wt % of the base material. Furthermore, the glass 31a preferably has a higher SiO ₂ content than ZnO. Specifically, the mass ratio of Si to Zn in the base material 31 (hereinafter referred to as the Si/Zn ratio) is preferably 3 or more, and more preferably 9 or more. The upper limit of the Si/Zn ratio is not particularly limited and can be, for example, 6000 or less, and is preferably 1200 or less.

It is preferable that the ZnO content and Si/Zn ratio satisfy the above ranges even when the substrate 31 contains other inorganic materials in addition to the glass 31a.

In addition to the above-described main components, the glass 31a may contain other components such as alkaline earth metal components, B ₂ O ₃ , and Al ₂ O ₃ . A combination of these other components may be added to the glass 31a. Here, alkaline earth metal elements collectively refer to Be, Mg, Ca, Sr, Ba, and Ra, and the term "alkaline earth metal component" in this embodiment refers to a compound containing an alkaline earth metal element. The glass 31a may contain one or more alkaline earth metal components. When an alkaline earth metal component is contained in the glass 31a, the alkaline earth metal component is preferably an oxide represented by the chemical formula MO, where M represents the alkaline earth metal element. In particular, it is preferable that one or more selected from CaO, SrO, and BaO be contained in the glass 31a as the alkaline earth metal component.

The content of the other components is not particularly limited. For example, the content of the alkaline earth metal component in the base material 31 can be 1 wt% or more and 50 wt% or less, and more preferably 5 wt% or more and 45 wt% or less, relative to 100 wt% of the base material. Furthermore, the content of B ₂ O ₃ in the base material 31 can be 0.1 wt% to 20 wt% relative to 100 wt% of the base material.

The glass 31a may also contain an alkali metal component. However, the alkali metal component may promote grain growth of the metal particles 33. Therefore, the content of the alkali metal component in the base material 31 is preferably 2 wt% or less relative to 100 wt% of the base material, and more preferably, the base material is substantially free of alkali metal components. "Substantially free of alkali metal components" means that the content of alkali metal components is less than 0.1 wt%. Note that alkali metals are a general term for Li, Na, K, Rb, Cs, and Fr, and "alkali metal components" in this embodiment refer to compounds containing alkali metal elements. Typically, alkali metal components contained in glass are Li ₂ O, Na ₂ O, K ₂ O, etc.

The content of the above-mentioned base material components can be analyzed using various component analysis methods, such as energy dispersive X-ray analysis (EDX), electron probe microanalyzer (EPMA), TEM electron beam diffraction, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and X-ray fluorescence analysis (XRF).

As described above, the substrate 31 may contain one or more non-glass materials, such as semiconductor compounds and dielectric compounds, in addition to the glass 31a. In this embodiment, it is particularly preferable that the substrate 31 contains zirconia (ZrO ₂ ) particles 31b as the non-glass material. In this case, the content of the zirconia particles 31b can be 0 wt% to 90 wt%, preferably 10 wt% to 80 wt%, and more preferably 10 wt% to 60 wt%, relative to 100 wt% of the substrate of the discharge inducing unit 13. The average particle size (D50) of the zirconia particles 31b is not particularly limited, and is preferably 2 μm or less, for example.

The zirconia particles 31b in the substrate can be identified, for example, by mapping analysis using EDX or EPMA. The average particle size of the zirconia particles 31b can be calculated by measuring the equivalent circle diameter of the particles identified by the above method.

The first external electrode 6 and the second external electrode 8 can each include a baked electrode layer, a resin electrode layer, a plated electrode layer, etc., and may be composed of a single electrode layer or a laminate of multiple electrode layers. Generally, a baked electrode layer or a resin electrode layer is formed as a base electrode in contact with the element body 10, and a single or multiple plated electrode layers are formed on the surface of that base electrode.

When a baked electrode layer is formed, the baked electrode layer contains, as a conductive material, Ag, Cu, Pd, Au, Ni, or an alloy containing at least one of these metal elements. It may also contain glass frit or oxide particles. When a resin electrode layer is formed, the resin electrode layer contains the same conductive material as the baked electrode layer, as well as a thermosetting resin. When a plated electrode layer is formed, the type and number of layers of the plated electrode layer can be determined taking into account the mounting method and usage environment of the transient voltage protection component 2. For example, the plated electrode layer can be formed using a combination of Ni/Sn plating, Cu/Ni/Sn plating, Ni/Pd/Au plating, Ni/Pd/Ag plating, or Ni/Ag plating.

Next, an example of a manufacturing method for the transient voltage protection component 2 will be described with reference to Figures 4 and 5.

First, a slurry for the insulator layer containing the components of the insulator layer 11 is prepared. Specifically, the slurry for the insulator layer is obtained by adding raw material powders such as inorganic compounds and glass frit to an organic vehicle containing an organic solvent and an organic binder and kneading them. The slurry is then applied to a PET film using a doctor blade method or the like and dried appropriately to obtain multiple green sheets. In this embodiment, the sheet on which the discharge portion pattern is printed is referred to as the first green sheet 110, and the sheet on which the discharge portion pattern is not printed is referred to as the second green sheet 111.

Next, the discharge inducing portion pattern 130 as shown in FIG. 4 is formed on the first green sheet 110 using the discharge inducing portion slurry. The discharge inducing portion slurry is obtained by kneading glass frit, which is the raw material for the glass 31a, non-glass ceramic powder such as semiconductor powder or zirconia powder, metal powder, and an organic vehicle. The discharge inducing portion pattern 130 may be formed by various printing methods such as screen printing, transfer methods, or coating methods.

Next, a conductor pattern 168 as shown in FIG. 4 is formed on the first green sheet 110 using discharge electrode paste. The discharge electrode paste is obtained by kneading conductive powder, the raw material for the discharge electrodes 16 and 18, with an organic vehicle. The conductor pattern 168 is formed along the X-axis direction so as to straddle the surface of the first green sheet 110 and the surface of the discharge inducing portion pattern 130. The conductor pattern 168 also has a slit S of a predetermined width on the surface of the discharge inducing portion pattern 130. This slit S is an interruption where the conductor pattern 168 is not printed, and becomes a gap G after firing. The conductor pattern 168 can be formed in the same manner as the discharge inducing portion pattern 130.

Next, a cavity pattern 150 is formed using a cavity lacquer on the first green sheet on which the discharge inducing portion pattern 130 and the conductor pattern 168 have been printed. The cavity lacquer contains an organic solvent and an organic binder that disappear during firing, and the cavity pattern 150 is used to form an internal space in the opposing portion of the discharge electrodes. As shown in Figure 4, the cavity pattern 150 is preferably formed to cover the discharge inducing portion pattern 130 and a portion of the conductor pattern 168 that will become the opposing portions 16b and 18b. Through the above process, a first green sheet 110 is obtained on which a discharge portion pattern including the discharge inducing portion pattern 130, the conductor pattern 168, and the cavity pattern 150 has been printed.

Next, a first green sheet 110 having a discharge portion pattern and multiple second green sheets 111 are stacked and pressed in the stacking direction to obtain a green chip 100. At this time, the first green sheets 110 are stacked between the second green sheets 111 as shown in FIG. 5. The number of second green sheets 111 stacked is not particularly limited, and the number of second green sheets 111 stacked above and below the first green sheet 110 may be different.

Note that for simplicity's sake, Figures 4 and 5 illustrate the process of forming a single green chip. However, in actual manufacturing processes, a green sheet that is larger in the X-Y plane than the element body 10 is typically prepared, and multiple discharge portion patterns are printed continuously on the surface of the green sheet. A mother laminate is then formed using the green sheet, and multiple green chips are obtained by cutting this mother laminate at predetermined intervals.

Next, the green chip 100 obtained in the above process is subjected to a firing process to obtain the element body 10. The firing conditions are not particularly limited, but for example, the holding temperature can be between 700°C and 950°C, and can also be set to a low temperature of between 700°C and 850°C. The temperature holding time during firing can be between 0.1 and 3 hours, and the firing atmosphere can be air, an inert gas, or a reducing atmosphere. During this firing process, the cavity pattern 150 disappears, and a cavity 15 is formed where the cavity pattern 150 was stacked. Note that a binder removal process may be performed as appropriate before the firing process, and if firing is performed in a reducing atmosphere, a reoxidation process may be performed after firing.

Next, a pair of external electrodes 6, 8 are formed on the surface of the element body 10 obtained in the above process. The method for forming the external electrodes 6, 8 is not particularly limited. For example, to form baked electrode layers as the external electrodes 6, 8, a conductive paste containing glass frit may be applied to the end surfaces of the element body 10, and then the element body 10 may be heat-treated under specified conditions (e.g., in air at 600-800°C for 1-5 hours). Alternatively, to form resin electrodes as the external electrodes 6, 8, a conductive paste containing a thermosetting resin may be applied to the end surfaces of the element body 10, and then the element body 10 may be heated to a temperature at which the thermosetting resin hardens. Furthermore, after forming baked electrodes or resin electrodes using the above method, the external electrodes 6, 8 may be formed with a multilayer structure by sputtering, vapor deposition, electrolytic plating, electroless plating, or the like.

Through the above manufacturing process, the transient voltage protection component 2 shown in Figure 1 is obtained.

(Summary of the embodiment)
In the transient voltage protection component 2 according to this embodiment, the base material 31 of the discharge inducing part 13 has glass 31a containing SiO ₂ and ZnO.

Discharge triggering sections containing glass components have been known for some time. However, when conventional glass in this field is used, excessive grain growth of metal particles occurs during high-temperature firing, making it easier for a pair of discharge electrodes to short-circuit through the discharge triggering section. On the other hand, if firing is performed at a low temperature of less than 850°C to prevent short-circuiting, the density of the discharge triggering section cannot be ensured, resulting in a decrease in ESD resistance.

As a result of extensive investigation, the inventors have found that the denseness of the discharge inducing part 13 can be ensured even with low-temperature firing by including ZnO in addition to _SiO2 in the glass 31a of the discharge inducing part 13. As a result, the transient voltage protection component 2 of this embodiment can obtain high ESD resistance while suppressing short-circuit defects with low-temperature firing.

In particular, by controlling the composition of the glass 31a within a predetermined range, the density of the discharge inducing portion 13 can be further improved, further increasing the ESD resistance. Specifically, the ZnO content in the substrate 31 is 0.05 wt% or more and 15 wt% or less, relative to 100 wt% of the substrate. In addition, the Si/Zn ratio of the substrate 31 is 3 or more. Since alkali metal components tend to promote grain growth of the metal particles 33, the content of alkali metal components in the substrate 31 is preferably 2 wt% or less, and more preferably, the substrate 31 is substantially free of alkali metal components.

In this embodiment, the discharge inducing part 13 contains zirconia particles 31b in addition to glass 31a. The inclusion of non-glass zirconia particles 31b in the base material 31 of the discharge inducing part 13 improves the dispersibility of the metal particles 33, further improving the ESD resistance. Furthermore, the zirconia particles 31b improve the adhesion of the discharge inducing part 13 to the insulator layer 11.

(Modification)
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways within the scope of the present invention.

For example, the pair of discharge electrodes 16, 18 may face each other in the Y-axis direction. In the transient voltage protection component 2a shown in Figure 6A, the side edge 16c of the first discharge electrode 16 along the Y-axis direction and the side edge 18c of the second discharge electrode 18 along the Y-axis direction face each other across a gap G. In other words, the side edges 16c, 18c facing the center of the element body are the facing parts, and discharge occurs between the side edges 16c and 18c.

If the pair of discharge electrodes 16, 18, the discharge inducing part 13, and the cavity 15 are considered to be a discharge unit, the element body 10 may include multiple discharge units. Also, the transient voltage protection component may not have a cavity 15, and the discharge inducing part 13 may fill the gap between the pair of discharge electrodes.

As shown in FIG. 6B, the element body 10 may include a coil 40. Furthermore, the element body 10 may include a capacitor unit. The capacitor unit can be constructed by stacking internal electrode layers between insulator layers 11.

The present invention will be explained in more detail below using specific examples, but the present invention is not limited to these examples. In Tables 1 to 3, samples marked with * are outside the scope of the present invention.

(Experiment 1)
In Experiment 1, transient voltage protection components according to Samples 1 to 12 were manufactured using glass having a predetermined composition. The manufacturing conditions other than the glass composition were the same for Samples 1 to 12. The manufacturing method for transient voltage protection component 2 in Experiment 1 will be described below.

First, a slurry for the insulator layer, a slurry for the discharge triggering part, a paste for the discharge electrode, and a lacquer for the cavity were prepared. To the slurry for the insulator layer, glass and zirconia were added as raw material powders for the insulator layer, along with an organic vehicle. To the slurry for the discharge triggering part, an organic vehicle, glass frit with a specified composition, and Pd powder with an average particle size (D50) of 0.5 μm were added. In this slurry for the discharge triggering part, the blending ratio of glass frit to Pd powder was the same for all samples 1 to 12 in Experiment 1. To the paste for the discharge electrode, an organic vehicle and Pd powder, a conductive powder, were added.

Next, a green sheet was prepared using the above-mentioned insulator layer slurry. Then, the discharge inducing portion slurry, discharge electrode paste, and cavity lacquer were applied to the green sheet in the order listed to form the discharge portion pattern.

Next, green sheets printed with discharge pattern and green sheets without discharge pattern were stacked in a specified order and pressed in the stacking direction to obtain a mother laminate. The mother laminate was then cut to obtain multiple green chips for each sample.

Next, the green chip was fired in air for 0.5 hours to obtain a sintered body. For samples 1 to 3, some samples were fired at 750°C and others at 850°C, while for samples 4 to 12, the firing temperature was all 750°C. After the firing process, a conductive paste containing Ag was applied to the outer surface of the body, and the body was heated at 700°C for 1 hour to form a fired electrode containing Ag. Through these processes, a transient voltage protection component with the structure shown in Figures 1 to 2B was obtained.

The dimensions of the element were 1 mm width in the X-axis direction, 0.5 mm width in the Y-axis direction, and 0.5 mm height in the Z-axis direction. The average thickness of the discharge inducing portion was 5 μm, the average thickness of the discharge electrodes was 5 μm, and the width of the gap G, which is the distance between the opposing discharge electrodes, was 50 μm.

In Experiment 1, the transient voltage protection components obtained using the above manufacturing process were evaluated as follows:

(Analysis of the discharge triggering part)
The cross sections of the transient voltage protection components were observed using an SEM to measure the average particle size (D50) and content of metal particles contained in the discharge triggered section. It was confirmed that the average particle size of the metal particles in all samples was within the range of 0.1 μm to 2.0 μm, and the content of metal particles in the discharge triggered section was within the range of 15 to 25 vol%. The components of the substrate contained in the discharge triggered section were also analyzed.

(Porosity)
The porosity was measured to evaluate the density of the discharge triggered portion. Specifically, the slurry for the discharge triggered portion used in the manufacture of each example was fired under the same conditions as those for firing the green chip to prepare a plate-shaped sample (10 mm x 10 mm x 5 mm) of the discharge triggered portion. The porosity of the plate-shaped sample was then measured by Archimedes' method. This measurement was performed on five plate-shaped samples for each example, and the average value was calculated as the porosity of the discharge triggered portion. When the discharge triggered portion was manufactured by low-temperature firing at 750°C, a porosity of 8% or less was considered acceptable, and a porosity of 4% or less was considered good.

(ESD tolerance)
The ESD resistance of each sample was measured by the electrostatic discharge immunity test specified in IEC 61000-4-2. When manufactured by low-temperature firing at 750°C, ESD resistance of 10 kV or more was judged as pass, and 16 kV or more was judged as good.

The evaluation results of each sample in Experiment 1 are shown in Table 1.

As shown in Table 1, when sample 1, which does not contain ZnO, was manufactured by low-temperature firing at 750°C, the porosity of the discharge triggered portion was high and the pass/fail criteria for ESD resistance were not met. On the other hand, samples 2 to 12, even when manufactured by low-temperature firing at 750°C, had lower porosity and higher ESD resistance than sample 1. These results show that when the glass of the discharge triggered portion contains SiO ₂ and ZnO, the density of the discharge triggered portion can be improved and high ESD resistance can be obtained, even when manufactured by low-temperature firing.

Furthermore, samples 3 to 7 had lower porosity and higher ESD resistance than sample 2, which had a lower ZnO content. Samples 3 to 7 also had higher ESD resistance than sample 8, which had a higher ZnO content. Samples 3 to 7 also had better porosity and ESD resistance than the high-temperature fired sample 1 (samples 1-2). These results suggest that the ZnO content should preferably be between 0.05 wt% and 15 wt% relative to 100 wt% of the substrate. It also suggests that the Si/Zn ratio of the substrate should preferably be 3 or greater.

Furthermore, the results for samples 9 to 12 showed that the alkaline earth metal component contained in the glass can be one type or multiple types.

(Experiment 2)
In Experiment 2, glass and zirconia were added to the discharge triggered portion to manufacture transient voltage protection components according to Samples 21 to 23. The experimental conditions in Experiment 2 were the same as those in Experiment 1, except for the composition of the substrate in the discharge triggered portion, and Samples 21 to 23 in Experiment 2 were also evaluated in the same manner as in Experiment 1. The evaluation results of Experiment 2 are shown in Table 2.

From the results shown in Table 2, it was found that adding zirconia to the discharge triggered part in addition to the specified glass components can improve the density of the discharge triggered part and obtain a high ESD resistance. It was also found that the _ZrO2 content is preferably 60 wt% or less.

(Experiment 3)
In Experiment 3, transient voltage protection components according to Samples 31 to 33 were manufactured using glass containing predetermined components in addition to SiO ₂ and ZnO. Specifically, the glass of Samples 31 and 32 contained Na ₂ O as an alkali metal component, and the glass of Sample 33 contained B ₂ O _3. The experimental conditions in Experiment 3 were the same as those in Experiment 1, except for the glass composition, and Samples 31 to 33 of Experiment 3 were also evaluated in the same manner as in Experiment 1. The evaluation results of Experiment 3 are shown in Table 3.

The results for sample 31 shown in Table 3 indicate that when alkali metal components are present in glass, metal particle growth is more likely to occur, resulting in a decrease in ESD resistance. In contrast, the results for sample 32 indicate that if the alkali metal component content is 2 wt% or less relative to 100 wt% of the base material, the decrease in ESD resistance can be suppressed.

Furthermore, the results of Sample 33 show that even when glass containing B ₂ O ₃ in addition to SiO ₂ and ZnO is used, the density of the discharge inducing portion can be ensured and a high ESD resistance can be obtained.

2, 2a, 2b... transient voltage protection component 10... element body 10a... end face 10b... side face 10c... main surface 11... insulating layer 13... discharge inducing portion
31...Base material
31a ... Glass
31b... Zirconia particles
33... Metal particles 15... Cavity part 16... First discharge electrode
16a...Drawer part
16b...Opposing part 18...Second discharge electrode
18a...Drawer part
18a: opposing portion 6: first external electrode 8: second external electrode 100: green chip 110: first green sheet 130: pattern for discharge inducing portion 150: cavity pattern 168: conductor pattern 111: second green sheet

Claims (5)

a pair of discharge electrodes facing each other across a gap;
a discharge inducing unit adjacent to the pair of discharge electrodes,
the discharge inducing unit has a base material containing glass and a plurality of metal particles dispersed in the base material,
the glass contains SiO ₂ and ZnO ;
The content of the ZnO is 0.05 wt % or more and 15 wt % or less with respect to 100 wt % of the base material,
The Si/Zn ratio in the substrate is 3 or more.
Transient voltage protection components. 2. The transient voltage protection component of claim 1, wherein the glass contains an alkaline earth metal component and/or _{B2O3 .} The transient voltage protection component according to claim 1 or 2, wherein the substrate comprises zirconia. A transient voltage protection component according to any one of claims 1 to 3, wherein the ZnO content in the substrate is 0.05 wt% or more and 15 wt% or less, relative to 100 wt% of the substrate. 5. The transient voltage protection component according to claim 1 , wherein the content of the alkali metal component in the substrate is 2 wt % or less relative to 100 wt % of the substrate.