JPH11307312A - Laminated varistor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated varistor, in which the grain growth of the outer peripheral part of a laminated varistor can be suppressed, characteristic deterioration in a characteristic part due to the outer peripheral part can be prevented, and failures such as the mutual welding of laminates at burning can be prevented. SOLUTION: This is a laminated varister 1, in which ceramic layers 5 with ZnO as the main component and inside electrode layers 13 formed on the ceramic layers 5 are laminated on a laminate, and outside electrodes 17 are formed so as to be electrically connected with the inside electrode layers are formed on the laminate. The ceramic layers on which the inside electrode layers 13 are formed are constituted of characteristic parts 9 with varistor characteristics and outer peripheral parts 11 other than the characteristic parts, and at least one kind of oxide or compound selected from among Y, Ba, Sr, and rare earth elements are present in the outer peripheral parts 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laminated varistor,
And its manufacturing method.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of electronic devices and the speeding up of circuits, the elements used in these devices have been made into chips and higher frequencies. Under such circumstances, varistors serving as noise absorbing elements have also been formed into chips, and chip-type laminated varistors containing ZnO or SrTiO ₃ as a main component have appeared. Further, the stacked varistor is required to be further reduced in size and height for reasons such as higher circuit density.

In order to reduce the size and height of the laminated varistor, the surge resistance per electrode area is increased, or the number of layers is increased by reducing the particle size of the varistor material, thereby increasing the number of effective electrodes. It is necessary to increase the area. However, these methods have limitations, and it is necessary to solve the structural problems of the multilayer varistor in order to increase the surge resistance.

[0004] A structural problem in the conventional multilayer varistor is the outer peripheral portion around the characteristic portion where the varistor characteristics can be obtained. Specifically, it is as follows.

[0005] 1. In a normal laminating method, pressure is hardly applied to the outer peripheral portion during lamination and pressure-bonding, and the density is likely to be reduced due to the thickness of the internal electrode.

[0006] 2. During the firing, the growth of grains in the outer peripheral portion is promoted by diffusion of heat or oxygen, and the varistor voltage tends to be low.

[0007] Due to such a problem in the outer peripheral portion, the original characteristics of the characteristic portion are regulated, and as a result, the surge withstand capability is suppressed.

In order to solve such a problem, there is a multilayer varistor disclosed in Japanese Patent Application Laid-Open No. 5-29105. As shown in FIG. 4, the multilayer varistor 20 includes a ceramic layer 23, an internal electrode layer 24, and an external electrode 25, and a characteristic portion 21 for obtaining varistor characteristics and an outer peripheral portion 22 other than the characteristic portion 21. It is composed of Of these, Sb ₂ O ₃ or Zn ₇ Sb ₂ O ₁₂ is added to the outer peripheral portion 22 as a sub-component. With such a configuration, the grain growth of the particles of the ceramic layer at the outer peripheral portion is suppressed, the outer peripheral portion is made denser, and further, the varistor voltage is prevented from being reduced.

[0009]

In the conventional multilayer varistor, Sb ₂ O ₃ having a melting point as low as 656 ° C. is added as an auxiliary component to the outer periphery thereof. Pyrochlore is formed with ZnO as a main component. For this reason, there is an advantage that the diffusing power is strong. However, the probability of covering the connection between the internal electrode layer and the external electrode is high, and a contact failure is likely to occur. Further, there is a problem that the laminates may be welded to each other during firing.

SUMMARY OF THE INVENTION It is an object of the present invention to suppress the occurrence of grain growth in the outer peripheral portion of a multilayer varistor, prevent the outer peripheral portion from deteriorating characteristics given to a characteristic portion, and to prevent defects such as welding between laminated members during firing. It is an object of the present invention to provide a laminated varistor that can prevent the occurrence of the varistor.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above objects. According to a first aspect of the present invention, there is provided a multilayer varistor that is electrically connected to the internal electrode layer on a laminate in which a ceramic layer containing ZnO as a main component and an internal electrode layer formed on the ceramic layer are stacked. A multilayer varistor in which external electrodes are formed as described above, wherein the ceramic layer comprises a characteristic portion on which the internal electrode layer is formed and a varistor characteristic is obtained, and an outer peripheral portion other than the characteristic portion. Is characterized by the presence of at least one oxide or compound selected from Y, Ba, Sr and rare earth elements (hereinafter referred to as a grain growth inhibitor).

With such a configuration, it is possible to suppress the grain growth on the outer peripheral portion of the multilayer varistor, and to prevent an influence on the characteristic portion such as a decrease in surge withstand capability. In addition, by using the above oxide or compound, a solid phase reaction occurs with ZnO, which is a main component of the varistor material, and the insulating property near the surface of the outer peripheral portion can be increased. Furthermore, since these do not become a liquid phase, there is no fear of poor contact between the internal electrode and the external electrode, and it is possible to prevent the laminates from sticking during firing.

In the multilayer varistor of the second invention,
It is preferred ratios r ₁ / r ₂ of the average particle diameter r ₂ of the mean particle size r ₁ and the characteristic portion of the outer peripheral portion is 0.8 or less.

With such a particle size, the surge withstand capability of the multilayer varistor can be further improved.

A third aspect of the present invention is a method of manufacturing a multilayer varistor having a characteristic portion capable of obtaining varistor characteristics and an outer peripheral portion other than the characteristic portion. Or before firing and during firing,
It is characterized in that a grain growth inhibitor is present in the outer peripheral portion and diffused during firing.

[0016] By adopting such a method of manufacturing a laminated varistor, the above-mentioned grain growth inhibitor can be easily diffused to the outer peripheral portion of the laminated varistor, and the grain growth at the outer peripheral portion can be effectively suppressed, and the surge can be suppressed. A laminated varistor with improved resistance can be obtained.

In the method of manufacturing a multilayer varistor according to a fourth aspect of the present invention, it is preferable that the grain growth inhibitor is present in a portion corresponding to the outer peripheral portion by printing.

In the method for manufacturing a multilayer varistor according to a fifth aspect of the present invention, the grain growth inhibitor is attached to a surface of the multilayer body during balleting of the multilayer body including the characteristic portion and the outer peripheral portion. Preferably.

By coordinating the grain growth inhibitor in this manner, the grain growth inhibitor can be uniformly diffused to the outer peripheral portion, and the grain growth at the outer peripheral portion can be surely suppressed.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A laminated varistor according to the present invention comprises a laminated body obtained by laminating a ceramic layer comprising a characteristic portion and an outer peripheral portion and an internal electrode layer formed on the ceramic layer.
External electrodes are formed on the laminate.

Here, the ceramic layer used in the multilayer varistor of the present invention may be any one containing ZnO as a main component. Those containing no ZnO as a main component are not preferable because the reaction of the compound is not always insulating.

The characteristic portion of the ceramic layer is a portion where varistor characteristics are obtained, that is, a portion sandwiched by internal electrode layers having different polarities. Therefore, the portion where the internal electrode layer is formed is not always the characteristic portion. The outer peripheral portion of the ceramic layer indicates a portion other than the characteristic portion of the ceramic layer, and has a structure covering the characteristic portion.

The grain growth inhibitor to be diffused to the outer peripheral portion is formed into a paste before laminating the ceramic green sheets and is applied on the ceramic green sheets. , And diffused to the outer periphery during firing of the laminate. In addition, as a method of applying the grain growth inhibitor on the ceramic green sheet, screen printing, sputtering and the like can be mentioned.

Even if the grain growth inhibitor is diffused after firing, grain growth at the outer peripheral portion has already occurred after firing, and the particle size at the outer peripheral portion is not small, which is not preferable.

Next, the present invention will be described more specifically with reference to examples.

[0026]

(Embodiment 1) A method of manufacturing a multilayer varistor according to the present invention will be described. FIG. 1 is a schematic sectional view of a laminated varistor according to the present invention, and FIG. 2 is an exploded perspective view of the laminated body of the first embodiment. First, as a starting material of a varistor material to be a ceramic layer, ZnO as a main component, and
_{Bi 2 O 3 1.0mol%, MnO0.5mol} %, CoO0.
_{5mol%, SiO 2 1.0mol%,} B 2 O 3 0.1mol%, S
b ₂ O ₃ 0.5mol%, blended and Al ₂ O ₃ 100ppm, and the varistor material.

Next, the obtained varistor material is mixed and pulverized by a ball mill for 20 hours, dewatered, dried, and dried for 60 hours.
Granulation was performed using a mesh sieve to obtain a granulated product. 7
After calcining at 50 ° C. for 2 hours, the mixture was roughly pulverized, mixed and pulverized again with a ball mill to obtain a calcined powder. Further, a solvent, a binder, and a dispersant were added to the obtained calcined powder, and a thickness of 50 μm was added.
m. Next, the formed body was punched into a predetermined size to obtain a ceramic green sheet.

Next, as shown in FIG. 2, a Pt paste was printed on a part of the obtained ceramic green sheet 7 by a screen printing method to form an internal electrode layer 13.

Next, on the outer peripheral portion 11 of the ceramic green sheet 7 on which the internal electrode layer 13 is printed, excluding the characteristic portion 9,
BaTiO ₃ , SrTiO ₃ , Sb ₂ O ₃ , Y ₂ O ₃ , and a grain growth inhibitor 15 in the form of a paste of a rare earth oxide were screen-printed to a thickness of about 2 μm. The grain growth inhibitor 11 is screen-printed on the entire surface of one side of the ceramic green sheet 7 on which the internal electrode layer 13 is not printed in the above-described manner, and these two types of ceramic green sheets 7 are laminated in a predetermined order and direction. And a laminate 3.

Further, after the obtained laminate 3 was degreased at 500 ° C., it was baked at 900 ° C. for 3 hours to obtain a laminated sintered body. Then, as shown in FIG. 1, an external electrode 17 is formed by baking Ag paste at 800 ° C. on the side surface of the laminated sintered body including the ceramic layer 5 and the internal electrode layer 13 where the internal electrode layer 13 is exposed. The mold varistor 1 was used.

The surge resistance of the multilayer varistor obtained as described above, and the ratio r ₁ / r ₂ of the particle size r ₂ of the particle size r ₁ and the characteristic portion of the outer peripheral portion was measured and firing the laminate The presence or absence of welding at the time was examined. Table 1 shows the results. The surge withstand capability was measured after applying a voltage to the laminated varistor twice at 5 minute intervals and allowing the varistor to stand for 1 minute. Also, the particle diameter r of the outer peripheral portion
The particle size of ₁ and the particle size r ₂ of the characteristic part is determined after polishing the sample.
It was measured by thermal etching. Furthermore, S is added to the grain growth inhibitor.
Comparative examples using b ₂ O ₃ and those using no grain growth inhibitor were used as comparative examples.

[0032]

[Table 1]

As shown in Table 1, in the production method as described above, the one in which the grain growth inhibitor was coordinated and diffused in the outer peripheral portion was:
It can be confirmed that the surge resistance is significantly improved as compared with Comparative Example 2 in which no grain growth inhibitor was used. It should be noted that the use of Sb ₂ O ₃ as the grain growth inhibitor is not preferable because the laminates are welded to each other during firing.

(Embodiment 2) FIG. 1 is a schematic sectional view of a laminated varistor according to the present invention, and FIG. 3 is an exploded perspective view of a laminated body of Embodiment 2. As shown in FIG. 3, a Pt paste was printed on a part of the ceramic green sheet 7 obtained in the same manner as in Example 1 by a screen printing method to form an internal electrode layer 13.

Next, two types of ceramic green sheets 7, a ceramic green sheet 7 on which the internal electrode layer 13 is printed and a ceramic green sheet 7 on which the internal electrode layer 13 is not printed, are laminated in a predetermined order and direction. The laminate 3 was obtained.

Thereafter, the obtained laminated body 3 and BaTiO 3
₃ , SrTiO ₃ , Sb ₂ O ₃ , Y ₂ O ₃ , and a grain growth inhibitor consisting of a rare earth oxide are put together with a cobblestone in a polypot and rotated to perform balling, and at the same time, to the surface of the laminate 3 A growth inhibitor was deposited.

Further, the laminate 3 to which the grain growth inhibitor has been adhered is degreased at 500 ° C., and baked at 900 ° C. for 3 hours.
A laminated sintered body was obtained. Then, as shown in FIG. 1, an external electrode 17 is formed by baking an Ag paste at 800 ° C. on the side surface of the obtained laminated sintered body where the internal electrode layer 13 is exposed,
The laminated varistor 1 was used.

[0038] A multilayer varistor obtained as described above, similarly surge resistance as in Example 1, and the ratio r ₁ / r ₂ of the particle size r ₂ of the particle size r ₁ and the characteristic portion of the outer peripheral portion It was measured. Table 2 shows the results.

[0039]

[Table 2]

As shown in Table 2, even in the production method in Example 2, the grain growth inhibitor was diffused in the outer peripheral portion to suppress the grain growth in the outer peripheral portion. It can be confirmed that the surge immunity of the multilayer varistor is improved.

(Example 3) Among the laminated varistors manufactured using the same manufacturing method as in Example 1, the grain growth inhibitor was Y ₂ O ₃ , and the coating thickness was changed to change the grain size at the outer peripheral portion. The diameter was changed to change the outer peripheral part particle diameter / characteristic part particle diameter. Further, the surge withstand capability at that time was measured, and the results are shown in Table 3. Note that the asterisks in the table are outside the scope of the present invention.

[0042]

[Table 3]

[0043] Table as shown in 3, in claim 1, the ratio r between the average particle diameter r ₂ of the mean particle size r ₁ and the characteristic portion of the outer peripheral portion ₁ /
The reason for limiting the r ₂ to 0.8 or less, as in sample No. 44, the average particle diameter r ₁ and a ratio r ₁ / r ₂ of the average particle diameter r ₂ of the characteristic portion of the outer peripheral portion than 0.8 This is because if it is large, the surge withstand capacity is not increased, which is not preferable.

[0044]

The multilayer varistor of the present invention is electrically connected to an internal electrode layer on a laminate in which a ceramic layer mainly composed of ZnO and an internal electrode layer formed on the ceramic layer are stacked. This is a configuration in which external electrodes are formed in such a manner.
Among these, the ceramic layer is formed of a characteristic portion on which an internal electrode layer is formed and varistor characteristics are obtained, and an outer peripheral portion other than the characteristic portion. The outer peripheral portion includes at least one selected from Y, Ba, Sr, and a rare earth element. One type of oxide or compound is present.

The method of manufacturing a laminated varistor according to the present invention is characterized in that at least one oxide or compound selected from the group consisting of Y, Ba, Sr and a rare earth element is added to the outer periphery before firing or before firing and during firing. It is present and diffused during firing.

Since the above configuration or manufacturing method is adopted, a grain growth inhibitor is made to exist in the outer peripheral portion of the multilayer varistor and then diffused to suppress the occurrence of grain growth in the outer peripheral portion. Can prevent characteristic deterioration given to the characteristic portion, and also prevent problems such as welding of the laminates during firing.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a laminated varistor of the present invention.

FIG. 2 is an exploded perspective view showing a multilayer body in the multilayer varistor of the first embodiment.

FIG. 3 is an exploded perspective view showing a multilayer body in the multilayer varistor of the second embodiment.

FIG. 4 is a schematic sectional view showing a conventional laminated varistor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laminated varistor 3 laminated body 5 ceramic layer 7 ceramic green sheet 9 characteristic portion 11 outer peripheral portion 13 internal electrode layer 15 grain growth inhibitor 17 external electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenjiro Hatano 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Inside Murata Manufacturing Co., Ltd.

Claims (5)

[Claims] 1. A ceramic layer containing ZnO as a main component,
A multilayer varistor in which external electrodes are formed on a laminate obtained by laminating an internal electrode layer formed on the ceramic layer so as to be electrically connected to the internal electrode layer, wherein the ceramic layer is An internal electrode layer is formed, comprising a characteristic portion from which varistor characteristics are obtained and an outer peripheral portion other than the characteristic portion, wherein the outer peripheral portion has at least one oxide selected from the group consisting of Y, Ba, Sr, and a rare earth element. Alternatively, a laminated varistor characterized in that a compound is present. 2. The method according to claim ₁ , wherein a ratio r ₁ / r ₂ between the average particle diameter r ₁ of the outer peripheral portion and the average particle diameter r ₂ of the characteristic portion is 0.8 or less. Stacked varistor. 3. A method for manufacturing a laminated varistor having a characteristic portion capable of obtaining varistor characteristics and an outer peripheral portion other than the characteristic portion, wherein Y is applied to the outer peripheral portion before firing or before firing and during firing. , Ba, Sr, and a rare earth element, wherein at least one kind of oxide or compound is present and diffused during firing. 4. The multilayer varistor according to claim 3, wherein at least one oxide or compound selected from the group consisting of Y, Ba, Sr, and a rare earth element is present in a portion corresponding to the outer peripheral portion by printing. Manufacturing method. 5. The method according to claim 1, wherein at least one oxide or compound selected from the group consisting of Y, Ba, Sr, and a rare earth element is balleted in a laminate comprising the characteristic portion and the outer peripheral portion.
The method for manufacturing a multilayer varistor according to claim 3, wherein the multilayer varistor is attached to a surface of the multilayer body.