JPH04306804A - Laminated type varistor - Google Patents

Abstract

PURPOSE:To obtain a laminated type varistor on which a leakage current can be decreased without deterioration of varistor voltage and surge resistivity. CONSTITUTION:A laminated body 4 is formed by alternately stacking a semiconductor ceramic layer 2 and an inner electrode 3, and a laminated type varistor 1 is constituted in such a manner that non-linear voltage characteristics obtained on the interface between the aforesaid inner conductive film 3 and the semiconductor ceramic layer 2. In this case, an oxide of element, which is selected from at least one or more kinds of Co and rare-earth element, and an Mn oxide are added to the above-mentioned inner electrode 3. Also, the adding quantity of the aforesaid Co or rare-earth element should be 0.01 to 20wt.% in terms of Co2O3, or R2O3, (R indicates rare-earth element), and the adding quantity of Mn should be 0.01 to 20wt.% in termas of Mn3O4.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a multilayer varistor that functions as a voltage nonlinear resistor, and in particular, the present invention relates to a multilayer varistor that functions as a voltage nonlinear resistor. Regarding improvement.

0002

2. Description of the Related Art Generally, voltage nonlinear resistors (hereinafter referred to as varistors) whose resistance value changes nonlinearly in accordance with applied voltage are widely used as surge absorbing elements and voltage stabilizing elements. The electrical characteristics of such a varistor are I
/i=(V/Vi)a. The above I is the current flowing through the element, V is the applied voltage, and Vi is the voltage between the terminals when a current of iA flows through the element, which usually takes a value of 1 mA and is called the varistor voltage V1 mA. In addition, the above a is a voltage nonlinear coefficient, which indicates how the voltage is controlled when the varistor is incorporated into an electric circuit.
The larger the value, the better the voltage control. In addition, in the field of electronic equipment used in communication equipment and other devices in recent years, miniaturization, IC integration, and integration are progressing rapidly. There is a growing demand for higher voltage or lower voltage. To meet these demands, laminated type varistors have been proposed to replace the disk type (for example,
(See Publication No. 8-23921). This multilayer varistor has a structure in which semiconductor ceramic layers and internal electrodes are alternately stacked to form a laminate, and external electrodes are formed on both end faces of the laminate to be connected to one end face of each of the internal electrodes. It is something. According to this multilayer varistor, it is possible to reduce the number of grain boundaries between the internal electrodes without causing the crystal grains of the semiconductor ceramic layer to grow to a large size, so it is possible to realize a lower operating voltage. It can also be made smaller. Furthermore, as an improved version of the multilayer varistor, there is a multilayer varistor in which unconnected internal electrodes that are not connected to the external electrodes are disposed within the ceramic layer between the internal electrodes (see Japanese Patent Application No. 1-302496); Furthermore, a multilayer varistor (see Japanese Patent Application No. 1-304296) has been proposed in which a rare earth element is added to the internal electrodes. The structure in which non-connected internal electrodes are disposed between the internal electrodes has two or less grain boundaries in the ceramic sandwiched between the electrodes, so the variation in varistor voltage is reduced compared to the above-mentioned conventional publication. Furthermore, the varistor voltage can be reduced from 4 to 16
Although the voltage is as low as V, the surge resistance can be improved. In addition, in the structure in which a rare earth element is added to the internal electrode, this rare earth oxide diffuses into the grain boundaries of the ceramic during firing, which increases the oxygen diffusion rate and improves the electrical characteristics. .

0003

[Problems to be Solved by the Invention] By the way, conventional multilayer varistors in which varistor characteristics are obtained at the interface between the internal electrodes or the non-connected internal electrodes and the ceramic layer have excellent voltage limiting ability; There is a problem in that the leakage current is large. Here, in order to improve leakage current in a multilayer varistor, it is generally known to increase the amount of bismuth oxide added, for example. However, simply improving the composition of the element by increasing the amount of bismuth oxide added does not significantly improve the leakage current.

The present invention has been made in view of the above-mentioned conventional situation, and an object of the present invention is to provide a multilayer varistor that can reduce leakage current while lowering the varistor voltage.

[0005]

[Means for Solving the Problems] The inventors of the present invention have investigated the causes of the above-mentioned leakage current and found that the number of grain boundaries of ceramics sandwiched between internal electrodes or unconnected internal electrodes is 2 or less. We also know that pores are created near the interface between the internal electrode and the ceramic layer due to rare earth oxides diffusing into the grain boundaries during firing, and that discharge occurs in these pores, increasing leakage current. I found it. Here, increasing the number of grain boundaries mentioned above may cause variations in varistor voltage and deteriorate the ability to lower voltage.
It is difficult to increase the number of grain boundaries. On the other hand, when the distribution state of the rare earth elements was analyzed using a wavelength dispersive X-ray microanalyzer, it was found that the distribution state of the rare earth elements and the Mn contained in the element were
It was found that the distribution state of That is,
The rare earth element moves toward Mn in the device, forming a Mn-rare earth element reaction phase. Based on this analysis result, the inventors thought that if Mn was added to the internal electrode together with the rare earth element in advance, the rare earth element would exist near the interface without diffusing into the element, and conducted an actual experiment. went. As a result, it was confirmed that when Mn was added, the rare earth element did not diffuse and was present at the interface between the internal electrode and the ceramic layer, that is, in the pores. When the electrical characteristics of the multilayer varistor thus obtained were measured, it was found that the leakage current was significantly improved compared to the case where only rare earth elements were added to the internal electrodes. Furthermore, the varistor voltage, limiting voltage, and surge resistance are at approximately the same level, and the capacitance is reduced to less than half. Therefore, if the capacitance is set to the same value, the electrode area of the internal electrode can be secured more than twice that of the conventional one, and as a result, the surge resistance can be improved by about twice. Furthermore, in the above experiment, similar results were obtained when Co was added instead of the rare earth element.

[0006] Accordingly, the invention of claim 1 provides a laminate in which semiconductor ceramic layers and internal electrodes are alternately stacked to form a laminate, and voltage nonlinear characteristics are obtained at the interface between the internal electrodes and the semiconductor ceramic layer. The type varistor is characterized in that an oxide of at least one element selected from Co or rare earth elements and an oxide of Mn are added to the internal electrode. Further, the invention of claim 2 provides that the amount of Co or the rare earth element added is set to Co2 O3, R2
It is characterized in that the amount of Mn added is 0.01 to 20% by weight in terms of O3 (R: rare earth element), and the amount of Mn added is 0.01 to 20% by weight in terms of Mn3O4. Here, the reason why the amounts of Co and rare earth elements added and the amount of Mn added are limited will be explained. This is because if the amount of Co and rare earth elements added is less than 0.01% by weight, it is difficult to obtain the effect of improving leakage current, and furthermore, the capacitance cannot be reduced. Moreover, if it exceeds 20% by weight, these elements and M
This is because a thick reaction phase with n is formed at the interface, resulting in a very large limiting voltage. Furthermore, if the amount of Mn added is less than 0.01% by weight, it becomes impossible to prevent the diffusion of Co and rare earth elements, and as a result, the effect of improving leakage current becomes smaller. Moreover, if the amount exceeds 20% by weight, the reaction phase will become thick at the interface as described above. Furthermore, the multilayer varistor of the present invention has one end surface of the internal electrodes exposed alternately on the end surface of the laminate, or a non-connected internal electrode that is not connected to the external electrode and is built into the ceramic layer between the internal electrodes. In short, it can be applied to any device that obtains voltage nonlinearity characteristics at the interface between the semiconductor ceramic layer and the internal electrode.

[0007]

[Function] According to the multilayer varistor of the present invention, since Co or rare earth elements are added to the internal electrodes and Mn is also added, the Co and rare earth elements do not diffuse during firing and are bonded together with Mn to the internal electrodes and the ceramic layer. It exists near the interface of the pores and fills the pores, and as a result, leakage current due to discharge can be reduced. In this case, since leakage current can be reduced with the number of crystal grain boundaries of the ceramic being minimized, variations in varistor voltage and deterioration of voltage reduction will not occur. In addition, as explained in the above-mentioned configuration, the present invention can reduce the capacitance by half or less without deteriorating the characteristics such as varistor voltage, limiting voltage, and surge resistance. When the electrode area is set so that the capacitance is the same, the electrode area can be doubled or more, and a synergistic effect can be obtained in that the surge resistance can be improved accordingly.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be explained with reference to the drawings. Embodiment 1 FIGS. 1 to 3 are diagrams for explaining a multilayer varistor according to a first embodiment of the present invention. In the figure, numeral 1 indicates a multilayer varistor of this embodiment. This varistor 1 has a rectangular parallelepiped shape, and has left and right end surfaces of a sintered body 4 made by alternately laminating semiconductor ceramic layers 2 mainly composed of ZnO and internal electrodes 3 made of Pt, and firing them together. 4a, 4b
It is constructed by forming an external electrode 5 made of Ag. Further, one end surface 3a of each internal electrode 3 is located on the left side of the sintered body 4,
The right end faces 4a and 4b are alternately led out, and this end face 3a is electrically connected to the external electrode 5. Furthermore, other parts of each internal electrode 3 are located inside the ceramic layer 2 and enclosed within the sintered body 4. Note that ceramic layers 6 as dummy are provided on the upper and lower surfaces of the sintered body 4. Furthermore, the number of crystal grains 7 in the thickness direction of each semiconductor ceramic layer 2 sandwiched between the internal electrodes 3 is 2 or less.

Co or an oxide of a rare earth element is added to each of the internal electrodes 3, and the amount of this added is 0.01 in terms of Co2 O3 or R2O3 (R: rare earth element). It is within the range of ~20% by weight. Further, an oxide of Mn is added to the internal electrode 3, and the amount of Mn added is 0.0 in terms of Mn3O4.
The content is within the range of 1 to 20% by weight. Note that the amount of each of the above additives added is set so as not to exceed 30 wt% in total. As a result, as shown in FIG.
, rare earth element oxide 8 , and Mn oxide 9 are present near the interface with each ceramic layer 2 of the internal electrode 3 .

Next, a method for manufacturing the multilayer varistor 1 of this embodiment will be explained. First, ZnO, Bi2 O3,
Co2 CO3, MnO, Sb2 O3, and Cr
97.9 mol% and 0.5 mol of 2O3, respectively
%, 0.5 mol %, 0.5 mol %, 0.3 m
It was weighed so that the composition ratio was 0.3 mol % and 0.3 mol %, and was heated in a ball mill using ion-exchanged water for 24 hours.
A ceramic material was created by time mixing. Next, this was filtered, dried, and calcined at 800° C. for 2 hours, and then ground again to produce ceramic raw material powder. Next, an organic binder is added to and mixed with the pulverized ceramic raw material powder, and a green sheet with a thickness of 20 μm is formed using a reverse roller method. This is punched into a predetermined size and shape to form a large number of ceramic layers 2 and 6. It was created(
(See Figure 2). In addition, 5% of Pr2O3 selected from rare earth elements was added to a paste made by mixing Pt with a vehicle.
A conductive paste was prepared by adding 5% by weight of Mn3O4. This conductive paste is shown in Figure 2.
As shown in FIG. 2, internal electrodes 3 were formed by printing on the top surface of each ceramic sheet 2. Next, the internal electrodes 3 are laminated one after another so that the one end surfaces 3a are alternately located, and the ceramic layers 6 are laminated on the upper and lower surfaces respectively, and the layers are laminated by applying a pressure of 2 ton/cm2 in the thickness direction. A body was formed and cut to size. This results in a structure in which only one end surface 3a of the internal electrode 3 is exposed alternately on both end surfaces of the laminate, and the other portions are buried within the laminate. Next, the laminate was fired in air at a temperature of 1200° C. for 2 hours to obtain a sintered body 4. During this firing, the rare earth element, Mn, precipitates near the interface between the ceramic layer 2 and the internal electrode 3, filling the pores. Finally, after applying Ag paste to the left and right end surfaces 4a and 4b of the sintered body 4 where one end surface 3a of the internal electrode 3 is exposed, the external electrode 5 is formed by baking at a temperature of 700° C. for 10 minutes. In this way, the multilayer varistor 1 of this example was manufactured.

[0011]

[Table 1]

Multilayer varistor 1 thus obtained
, varistor voltage V1mA, limiting voltage ratio V2A/V1
mA, surge resistance A, insulation resistance value MΩ, and capacitance value pF were measured. The above insulation resistance is the resistance value of the element when a voltage of 50% of the varistor voltage is applied for 30 seconds. For comparison, Pr2O3 was used as the internal electrode.
Similar measurements were also performed on a conventional multilayer varistor to which 5% by weight of 5% by weight was added.

Table 1 shows the results. As is clear from the table, there is almost no difference between the inventive sample and the conventional sample, with varistor voltage of 4.2 to 4.1V, limiting voltage ratio of 1.5, and surge withstand capacity of 50A, and satisfactory characteristics were obtained. It is being Furthermore, in the conventional sample, the insulation resistance value was 0.
The leakage current is as low as 3MΩ and large. On the other hand, in the sample of the present invention, the insulation resistance value is as high as 2.2 MΩ, which indicates that the leakage current can be improved. Furthermore, in terms of capacitance, the inventive sample had a capacitance of 220 pF and the conventional sample had a capacitance of 510 pF.
It is less than 1/2 compared to

[0014]

[Table 2]

Table 2 shows P in the internal electrode 3 of this example.
The amounts of r2 O3 and Mn3 O4 added were 0 to 3.
Varistor voltage V when changed within the range of 0wt%
1mA, capacitance value pF, insulation resistance value MΩ, surge resistance A, and limiting voltage ratio V2A/V1mA. In the table, *marks are outside the scope of the present invention. As is clear from the table, when the amount of Pr2 O3 and Mn3 O4 added is 0 (see sample Nos. 1, 7, and 13), the insulation resistance value is low at 0.1 to 1.1 MΩ, and leakage is low. Current has not improved. Further, when the above-mentioned addition amount was 30 wt% (see Sample Nos. 6 and 12), although the leakage current was improved, the sash withstand capacity was degraded to 15 and 20 A. On the other hand, when the amounts of Pr2 O3 and Mn3 O4 added are 0.01 to 20 wt% (sample No. 2
~5,8~11), both have insulation resistance values of 2.1~2
．． It can be seen that satisfactory characteristics have been obtained for both, with a high surge resistance of 3MΩ and a surge resistance of 50A.

[0016]

[Table 3]

Table 3 shows that Co2 was used in the internal electrode 3 of this example.
When O3 and Mn3O4 are added and the amount of these added is varied within the range of 0 to 30 wt%,
Varistor voltage V1mA, capacitance value pF, insulation resistance value M
Ω, surge resistance A, and limiting voltage ratio V2A/V1mA are shown. In the table, *marks are outside the scope of the present invention. As is clear from the table, when the amount of Co2 O3 and Mn3 O4 added is 0 (see sample No. 1, 7, 13)
, all have low insulation resistance values of 0.1 to 1.1 MΩ. Moreover, when the above addition amount is 30 wt% (Sample No.
6, 12), and although the leakage current has been improved, the sash resistance has deteriorated to 15, 20A. On the other hand, each addition amount of Co2 O3 and Mn3 O4 is 0.01~
In the case of 20 wt% (Sample No. 2-5, 8-11
), the insulation resistance value is high at 2.0 to 2.3 MΩ, and the surge withstand capacity is 50 A, both of which have satisfactory characteristics, and almost the same effect is obtained when Co2 O3 is added. I understand.

Embodiment 2 FIGS. 4 and 5 are diagrams for explaining a multilayer varistor according to a second embodiment of the present invention. In the multilayer varistor 20 of this embodiment, semiconductor ceramic layers 21 and internal electrodes 22 are alternately laminated, and external electrodes 24 are formed on the left and right end surfaces 23a and 23b of a sintered body 23 that is integrally fired. death,
Furthermore, the semiconductor ceramic layer 2 between each of the internal electrodes 22 is
1, a non-connected internal electrode 25 is disposed within it. The peripheral end surface of each unconnected internal electrode 25 is covered with a ceramic layer 2.
The non-connected internal electrodes 25, which are not connected to the external electrodes 24, are interposed between the internal electrodes 22. In addition, 2
6 is a ceramic layer as a dummy.

Each of the internal electrodes 22 and the non-connected internal electrodes 25 are coated with Co or an oxide of a rare earth element and M.
n oxide is added, and the amounts added are in the range of 0.01 to 20% by weight and 0.01 to 20% by weight, respectively, in terms of Co2 O3 or R2 O3 (R: rare earth element). It is inside.

Next, a method of manufacturing the multilayer varistor 20 of this embodiment will be explained. First, ZnO, Bi2 O3
, Co2 CO3, MnO, Sb2 O3, and Cr
97.9 mol% and 0.5 mol of 2O3, respectively
%, 0.5 mol %, 0.5 mol %, 0.3 m
It was weighed so that the composition ratio was 0.3 mol % and 0.3 mol %, and was heated in a ball mill using ion-exchanged water for 24 hours.
A ceramic material was created by time mixing. Next, this was filtered, dried, and calcined at 800° C. for 2 hours, and then ground again to produce ceramic raw material powder. Next, an organic binder is added to and mixed with the pulverized ceramic raw material powder, and a green sheet with a thickness of 20 μm is formed using a reverse roller method. This is punched out into a predetermined size and shape to form a large number of ceramic sheets 21a, 26. (see Figure 5). In addition, Pr2 selected from rare earth elements is added to the paste made by mixing Pt with a vehicle.
A conductive paste was prepared by adding 5% by weight of O3 and further adding 5% by weight of Mn3O4. This conductive paste is applied to each ceramic sheet 21a as shown in FIG.
The internal electrodes 22 and non-connected internal electrodes 25 were formed by printing on the upper surface of the . Next, the internal electrodes 22 are laminated in order so that one end surface thereof is alternately located and the non-connected electrodes 25 are located between the internal electrodes 22, and ceramic layers 26 are superimposed on the upper and lower surfaces of these, respectively. 2 tons in the thickness direction of this
A pressure of /cm2 was applied to form a laminate, which was cut into predetermined dimensions. As a result, only one end surface of the internal electrode 22 is exposed alternately on both end surfaces of the laminate, and the other portions of the internal electrode 22 and the unconnected internal electrode 25 are enclosed within the laminate. Next, the laminate was fired in air at a temperature of 1200° C. for 2 hours to obtain a sintered body 23. Finally, Ag paste is applied to the left and right end faces 23a and 23b of the sintered body 23, where one end face of the internal electrode 22 is exposed, and then baked at a temperature of 700°C for 10 minutes to form the external electrode 24.
was formed, thereby manufacturing the multilayer varistor 20 of this example.

[0021]

[Table 4]

Multilayer varistor 2 thus obtained
0, varistor voltage V1mA, limiting voltage ratio V2A/V
1 mA, surge resistance A, insulation resistance value MΩ, and capacitance value pF were measured. For comparison, similar measurements were also performed on a conventional multilayer varistor in which only 5% by weight of Pr2O3 was added to the internal electrodes. Table 4 shows the results. As is clear from the table, both the inventive sample and the conventional sample have satisfactory characteristics such as a varistor voltage of 12.0 V, a limiting voltage ratio of 1.4, and a surge withstand capacity of 50 A. Furthermore, while the conventional sample had an insulation resistance value of 5.5 MΩ, the inventive sample had an improved insulation resistance value of 10 MΩ, indicating that the leakage current was improved. Furthermore, in terms of capacitance, the sample of the present invention has a capacitance of 10
0 pF, which is less than half of the 240 pF of the conventional sample.

[0023]

As described above, according to the multilayer varistor according to the present invention, since Co or a rare earth element oxide is added to the internal electrode, and an Mn oxide is also added, Co
, Rare earth elements exist together with Mn at the interface between the internal electrode and the ceramic layer and fill the pores, which has the effect of reducing leakage current without deteriorating the varistor voltage or surge resistance, and is also superior to conventional multilayer varistors. If the electrode area is set so that the capacitance is the same, the surge resistance can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining a multilayer varistor according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view of the multilayer varistor of the above embodiment.

FIG. 3 is a schematic diagram showing a state in which a rare earth element, Mn, is present in the internal electrode of the above example.

FIG. 4 is a cross-sectional view for explaining a multilayer varistor according to a second embodiment of the present invention.

FIG. 5 is an exploded perspective view of the multilayer varistor of the above embodiment.

[Explanation of symbols]

1,20 Laminated varistor 2, 21 Semiconductor ceramic layer 3,22 Internal electrode 25 Unconnected internal electrode 4,23 Sintered body (laminate)

Claims (2)

[Claims] 1. A multilayer varistor in which semiconductor ceramic layers and internal electrodes are alternately stacked to form a laminate, and a voltage nonlinear characteristic is obtained at the interface between the internal electrode and the semiconductor ceramic layer, A multilayer varistor, wherein the electrode is made of a metal material containing an oxide of at least one element selected from Co or rare earth elements, and an oxide of Mn. 2. In claim 1, Co or the rare earth element is 0.01 to 20% by weight in terms of Co2 O3 or R2 O3 (R: rare earth element), and Mn is M
A laminated varistor characterized in that n3O4 is contained in an amount of 0.01 to 20% by weight, and the total content is 30% by weight or less.