JP2016225404A - Sintered body for zinc oxide-based varistor, multilayer substrate including the same, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered body for a zinc oxide-based varistor having sufficient characteristics without using a rare earth element and a multilayer substrate including the same.SOLUTION: The sintered body for a zinc oxide-based varistor includes zinc oxide as a main component, contains a bismuth oxide of 0.9 to 1.2 mol% in terms of Bi, and a cobalt oxide of 1.0 to 1.5 mol% in terms of Co. The content of RM (RM is Sb, a rare earth element, Li, V, Ga, Zr, Ta, Cr, Ge, Nb, Te, W, Mn, Se, Mo, Cs, Re, Rb, Pd, Ba, Pt, Ti, Ni, Sr, In, Hf, Tl) and Sn is less than or equal to an impurity level.SELECTED DRAWING: Figure 1

Description

  The present invention uses a sintered body for a zinc oxide varistor, a multilayer substrate using the sintered body for a zinc oxide varistor, a method for producing a sintered body for a zinc oxide varistor, and a sintered body for a zinc oxide varistor. The present invention relates to a method for manufacturing a multilayer substrate.

Electronic devices such as computers and mobile phones incorporate ESD (electrostatic discharge) protection devices such as varistor elements in order to protect the electronic circuits and elements contained therein from abnormally high voltages caused by static electricity and noise. .
The varistor element exhibits a large electric resistance value when the applied voltage is low, and only a small amount of current flows. However, when the applied voltage increases, the electric resistance decreases remarkably and non-linearity where a large amount of current flows. A varistor (varistor material) showing resistance is used. Among these varistors, since desired characteristics can be easily obtained, zinc oxide varistors (zinc oxide varistor materials) containing zinc oxide as a main component and adding oxides other than zinc oxide are often used. Yes.
By incorporating a varistor element using a zinc oxide varistor material, especially a sintered body for a zinc oxide varistor obtained by sintering the same material, into the electronic circuit, high voltage due to static electricity or noise may be generated in a part of the electronic circuit. Even if the resulting current flows, it is possible to suppress such a large current from flowing in a desired part and a desired element of the electronic circuit.

However, on the other hand, the space occupied by the varistor elements is a factor that hinders downsizing of these electronic devices.
In order to solve this problem, for example, Patent Document 1 discloses that an ESD (electrostatic discharge) protection device is integrally formed with an electrode in a multilayer substrate as LTCC (low temperature co-fired ceramics).

It is desirable to use silver (Ag) having a low electrical resistance for the electrode used in contact with the LTCC. However, when silver is heated to a high temperature such as 1000 ° C. or higher, the performance as an electrode is degraded due to oxidation or the like.
For this reason, a laminate including a mixed raw material sheet (green sheet) of varistor material, on which an electrode material made of silver is formed, is baked at a temperature in the range of about 850 ° C. to 950 ° C. to varistor element (ESD protection device Are disclosed in Patent Literatures 2 to 6.

International Publication No. 2009/136535 JP 2010-238882 A JP 2007-5499 A JP-A-9-312203 JP 2012-114443 A JP-A-2005-97070

  Many of these conventional varistor materials (sintered varistors) have rare earth elements such as antimony (Sb), yttrium (Y) or praseodymium (Pr) as additives, titanium (Ti), nickel ( By using rare metals such as Ni), indium (In), vanadium (V), zirconium (Zr), niobium (Nb), and tungsten (W), a predetermined varistor characteristic such as non-linear resistance is obtained. Yes. However, rare metals, especially rare earth elements, are stable over a long period of time because their abundance on the earth is low, their production areas are limited, and it is difficult to extract and refine them technically and economically. There is a concern about the supply, and the price is high and the fluctuation is large. Further, antimony (Sb) is a toxic element. For this reason, a sintered body for zinc oxide varistors having sufficient characteristics without using these antimony (Sb) and rare earth elements, and minimizing the amount and types of other rare metals used, and the same were used. A multilayer substrate has been desired.

Moreover, the following was calculated | required also about the manufacturing method.
As described above, it is possible to obtain a sintered body for varistor (hereinafter, simply referred to as “sintered body”) by firing at a firing temperature of about 850 ° C. to 950 ° C. and lower than 1000 ° C. It was known. However, these conventional methods require heat treatment before firing in a temperature range of about 850 ° C. to 950 ° C. In this heat treatment, for example, two or more kinds of raw materials such as oxides used for forming a varistor sintered body having a desired composition are mixed and heated to 300 ° C. or higher.
And it baked in the temperature range of about 850 degreeC-950 degreeC using the raw material which performed this mixing and heat processing, and another kind of raw material added as needed, and obtained the sintered compact.
The inclusion of the two heating steps of heat treatment and firing not only complicates the steps, but also leads to an increase in energy consumption, and there has been a demand for omitting the heat treatment step.

The present invention minimizes the amount and type of rare metal used, and in particular, a sintered body for a zinc oxide varistor having sufficient characteristics without using antimony (Sb) and rare earth elements, and a multilayer substrate using the same. The purpose is to provide.
In addition, the present invention minimizes the amount and type of rare metal used, and in particular, does not use antimony (Sb) or rare earth elements, and performs firing at a temperature lower than 1000 ° C. without performing heat treatment in advance. It is an object of the present invention to provide a method for producing a zinc oxide varistor and a method for producing a multilayer substrate including an oxide varistor that can have sufficient characteristics.

  Aspect 1 of the present invention contains zinc oxide as a main component, bismuth oxide is 0.9 to 1.2 mol% in terms of bismuth (Bi), and cobalt oxide is 1.0 to 1.5 mol% in terms of cobalt (Co). RM (RM is antimony (Sb), rare earth element, lithium (Li), vanadium (V), gallium (Ga), zirconium (Zr), tantalum (Ta), chromium (Cr), germanium (Ge), niobium (Nb), tellurium (Te), tungsten (W), manganese (Mn), selenium (Se), molybdenum (Mo), cesium (Cs), rhenium (Re), rubidium (Rb), palladium (Pd), barium (Ba), platinum (Pt), titanium (Ti), nickel (Ni), strontium (Sr), indium (In), hafnium (Hf), thallium (T )), And a varistor sintered body wherein the content of tin (Sn) is less than an impurity level.

  In this specification, the metal element conversion when defining the composition means the content of the metal when “the whole metal element is 100 mol%”, and “the whole metal element is 100 mol%. “Do” means “the whole metal element including semimetals such as Si, B and Sb is made 100 mol%”. Further, “impurity level or lower” means that it contains zero or an amount recognized as an impurity level or an amount lower than that. Specifically, for example, when the entire metal element is 100 mol% It is 0.01 mol% or less, preferably 0.005 mol% or less. For practical measurement, for example, if it is below the detection limit (100 ppm by mass ratio) of an ICP (inductively coupled plasma) wet analyzer, the condition of 0.01 mol% or less is satisfied.

  Aspect 2 of the present invention includes, in order, a first insulating layer, a varistor layer that is the sintered body for a varistor according to aspect 1, a second insulating layer, and a first varistor disposed on the main surface of the varistor layer. A multilayer substrate having one internal electrode and a second internal electrode.

  Aspect 3 of the present invention includes a first insulating layer, a second insulating layer, and a third insulating layer, which are sequentially stacked, and the second insulating layer is provided therein. A multilayer substrate comprising: a varistor layer that is a sintered body for a varistor according to 1; and a first internal electrode and a second internal electrode arranged on a main surface of the varistor layer. It is.

  Aspect 4 of the present invention is as follows: 1) At least zinc oxide, bismuth oxide, and cobalt oxide are mixed without being subjected to heat treatment, zinc oxide is the main component, and bismuth oxide is converted to bismuth (Bi) in terms of 0.00. A step of obtaining a mixed raw material containing 9 to 1.2 mol%, cobalt oxide in an amount of 1.0 to 1.5 mol% in terms of cobalt (Co), and containing RM and tin (Sn) at an impurity level or less, and 2) And a step of firing the mixed raw material at 850 ° C. to 950 ° C., which is a method for producing a sintered body for varistors.

  Aspect 5 of the present invention is as follows: 1) At least zinc oxide, bismuth oxide, and cobalt oxide are mixed without being subjected to heat treatment, zinc oxide is the main component, and bismuth oxide is converted to bismuth (Bi) in terms of 0.00. A step of obtaining a mixed raw material containing 9 to 1.2 mol%, cobalt oxide in an amount of 1.0 to 1.5 mol% in terms of cobalt (Co), and containing RM and tin (Sn) at an impurity level or less, and 2) A step of disposing a first electrode material on a first insulating sheet made of an insulating material; 3) a step of forming a mixed raw material sheet containing the mixed raw material on the first electrode material; 4) a step of disposing a second electrode material on the mixed raw material sheet, 5) a step of forming a second insulating sheet made of an insulating material on the second electrode material, and 6) The first insulating sheet, and the mixed raw material sheet; A method for manufacturing a multilayer substrate, characterized in that it and a step of firing the second insulating sheet 850 ° C. to 950 ° C..

In the sintered body for a zinc oxide varistor according to the present invention and a multilayer substrate using the same, the amount of rare metal used and the type to be used are minimized, and particularly excellent without using antimony (Sb) or rare earth elements. Can have varistor characteristics.
In the manufacturing method according to the present invention, a sintered body for zinc oxide varistor and a zinc oxide varistor having sufficient varistor characteristics by firing at a temperature lower than 1000 ° C. without performing heat treatment in advance. A multilayer substrate including a sintered body can be manufactured.

Fig.1 (a)-FIG.1 (c) are model perspective views which illustrate the method of obtaining the sintered compact for varistors using a slurry-form mixed raw material. 2A is a perspective view showing the multilayer substrate 100, and FIG. 2B is a cross-sectional view showing the XIVb-XIVb cross section of FIG. 2A. FIG. 3A to FIG. 3D are perspective views showing a method for manufacturing the laminate 150. FIG. 4 is a perspective view showing the laminate 160. FIG. 5 is a diagram showing a method for manufacturing the multilayer substrate 100. 6A is a perspective view showing the multilayer substrate 200, and FIG. 6B is a cross-sectional view showing the XVIIIb-XVIIIb cross section of FIG. 6A.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, terms indicating a specific direction and position (for example, “up”, “down”, “right”, “left” and other terms including those terms) are used as necessary. These terms are used for easy understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meaning of these terms. Moreover, the part of the same code | symbol which appears in several drawing shows the same part or member.

  The present inventors use conventional antimony (Sb) and / or rare earth elements for varistors without using antimony (Sb) and rare earth elements and minimizing the amount and type of other rare metals used. In order to obtain a sintered body for varistors having a varistor characteristic (varistor voltage, insulation resistance and / or non-linear resistance) equal to or higher than that of the sintered body, intensive research was conducted. As a result, the present inventors have found a composition of bismuth oxide in a sintered body for zinc oxide varistor (containing zinc oxide as a main component (that is, containing 90 mol% or more of zinc oxide in terms of zinc (Zn))). Antimony (Sb) by not containing rare metals other than bismuth (Bi) and cobalt (Co) and further containing no tin (Sn) (below the impurity level) by being within the limited range. Further, the present inventors have found that a sintered body for varistors having excellent varistor characteristics can be obtained without containing rare earth elements, and have led to the present invention.

More specifically, the sintered body for a varistor according to the present invention that can be used as a varistor has zinc oxide as a main component, bismuth oxide in terms of bismuth (Bi), 0.9 to 1.2 mol%, and cobalt oxide. It contains 1.0 to 1.5 mol% in terms of cobalt (Co).
Furthermore, in the sintered body for varistors according to the present invention, the contents of RM and tin (Sn) are below the impurity level.

  In the manufacturing method according to the sintered body for varistors of the present invention, the sintered body (varistor material) obtained after firing is mainly composed of zinc oxide, and bismuth oxide is converted to 0.9 to 1.2 mol in terms of bismuth (Bi). %, After obtaining the mixed raw material so as to have a composition containing 1.0 to 1.5 mol% of cobalt oxide in terms of cobalt (Co), the mixed raw material is fired at 850 ° C. to 950 ° C.

  Moreover, in a preferred embodiment according to the method for producing a sintered body for varistors of the present invention, at least zinc oxide, bismuth oxide, and cobalt oxide are mixed without performing heat treatment, and zinc oxide is a main component, It contains 0.9 to 1.2 mol% bismuth oxide in terms of bismuth (Bi), 1.0 to 1.5 mol% cobalt oxide in terms of cobalt (Co), and the content of RM and tin (Sn) is below the impurity level. After obtaining the mixed raw material, the mixed raw material is fired at 850 ° C. to 950 ° C.

  That is, in the preferred embodiment, before obtaining the mixed raw material, two or more of a plurality of types of oxides (raw material powder) to be used (some types of the plurality of types of oxides are 2 It has substantially the same composition as the sintered body for the varistor to be obtained without pre-mixing and performing a heat treatment (for example, a heat treatment called “calcination”) that is heated to 300 ° C. or higher. A mixed raw material is obtained. And the mixed raw material which concerns on this preferable embodiment is baked at 850 degreeC-950 degreeC.

Below, the detail of the manufacturing method which concerns on the sintered compact for varistors which concerns on this invention, and the sintered compact for varistors is demonstrated.
1. Sintered body for varistor As described above, the sintered body for varistor (sintered body) according to the present invention contains zinc oxide as a main component, and bismuth oxide is 0.9 to 1.2 mol% in terms of bismuth (Bi). Cobalt oxide is contained in an amount of 1.0 to 1.5 mol% in terms of cobalt (Co), and the contents of RM and tin (Sn) are not more than the impurity level.
Thus, by limiting the composition to a narrow range, the sintered body for varistors obtained even when the mixed raw material is fired at 850 ° C. to 950 ° C. exhibits sufficient varistor characteristics such as having a high nonlinear constant.
And it can be fired at a temperature of less than 1000 ° C. in this way, in a state where silver (Ag) serving as an electrode is disposed on a mixed raw material sheet layer (green sheet layer) containing the mixed raw material powder. This means that the raw material sheet can be fired. For this reason, a multilayer substrate in which a silver electrode and a sintered body for varistor (varistor layer obtained by firing mixed powder) are integrally formed can be obtained.

1-1. Composition The reason why such a narrow composition range should be set for each element is shown below. However, these reasons indicate the reason why the inventor considered reasonable based on the knowledge obtained at the present time, and the technical scope of the present invention such as the composition defined by the claims is described. It should be noted that no further limitation is intended.
Note that the molar ratio of the oxide content in this specification does not take into account the oxygen atoms contained in the oxide, but considers only the atoms (metal element atoms) that are linked to oxygen. It is what I asked for. The metal element includes a semimetal such as boron, silicon, and antimony.

(1) Zinc oxide Zinc oxide is a material that is a base of the sintered body for varistor (varistor layer) of the present invention, and is a main component. That is, the sintered body for varistors of the present invention contains 90 mol% or more of zinc oxide in terms of zinc (Zn).
Preferably, the sintered body for varistors of the present invention contains 95 mol% or more of zinc oxide in terms of zinc (Zn).

(2) Bismuth oxide The sintered body for varistors of the present invention contains bismuth oxide in an amount of 0.9 to 1.2 mol%, preferably 1.0 to 1.2 mol% in terms of bismuth (Bi).
Bismuth oxide (bismuth) promotes densification of the sintered body even at a relatively low firing temperature of 850 ° C. to 950 ° C. Further, as a result of observing the microstructure of the material of the present invention by EDX (energy dispersive X-ray spectroscopy), bismuth oxide (bismuth) is segregated at the grain boundary of zinc oxide, and thereby a high resistance semiconductor grain boundary. It is considered that this produces a varistor characteristic as a double Schottky barrier. If the content of bismuth oxide is less than 0.9 mol% in terms of bismuth, this effect cannot be obtained sufficiently, and if it exceeds 1.2 mol%, a thick insulating layer mainly composed of bismuth oxide is formed. is there.

(3) Cobalt oxide The sintered body for varistors of the present invention contains 1.0 to 1.5 mol% of cobalt oxide in terms of cobalt (Co).
As a result of observing the element distribution in the sintered body for varistors of the present invention by EDX (energy dispersive X-ray spectroscopy), cobalt is uniformly present at both the grain boundaries and within the grains, and the zinc oxide particles are obtained by sintering. It was confirmed that the solid solution. Since solid solution cobalt can be changed from a divalent ion to a trivalent ion, it is considered to be a donor that emits electrons. The expression of varistor characteristics in zinc oxide-based varistors is based on the double Schottky barrier formed at the grain boundary. The double Schottky barrier is trapped at the grain boundary level that is considered to exist at the crystal grain boundary of zinc oxide. It is known that it is determined by the balance between the density of generated electrons and the ionized donor density in the grains, and when the content of bismuth oxide is in the above range, the content of cobalt oxide is 1.0 to When this balance is suitable at 1.5 mol%, it is considered that the effect of increasing the nonlinear constant of the varistor sintered body of the present invention is brought about.

(4) RM
The sintered body for varistors of the present invention is composed of RM (RM is antimony (Sb), rare earth element, lithium (Li), vanadium (V), gallium (Ga), zirconium (Zr), tantalum (Ta), chromium ( Cr), germanium (Ge), niobium (Nb), tellurium (Te), tungsten (W), manganese (Mn), selenium (Se), molybdenum (Mo), cesium (Cs), rhenium (Re), rubidium ( Rb), palladium (Pd), barium (Ba), platinum (Pt), titanium (Ti), nickel (Ni), strontium (Sr), indium (In), hafnium (Hf), thallium (Tl)) The amount is not more than the impurity level, that is, the content of each element is 0.01 mol% or less when the entire metal element is 100 mol%. Properly is less than 0.005mol%. Hereinafter, each element of RM will be described in detail focusing on antimony (Sb) and rare earth elements.

・ Antimony (Sb)
In many conventional sintered bodies for zinc oxide varistors, antimony (Sb) has been positively added to obtain good varistor characteristics. This is because by using antimony (Sb), the effect of adding other additives can be controlled well. However, antimony (Sb) has a problem that it has toxicity as described above.
The sintered body for varistors according to the present invention contains antimony (Sb) only at an impurity level or lower.

-Rare earth elements In many conventional sintered bodies for zinc oxide varistors, rare earth elements were intentionally added to improve varistor characteristics.
However, the sintered body for varistors according to the present invention contains zero rare earth element or less than the impurity level. That is, for each of the rare earth elements, the total amount of the metal elements is about 0.01 mol% or less, and the total rare earth elements is about 0.05 mol% or less. Preferably, it is 0.005 mol% or less for each of the rare earth elements, and the total rare earth elements is 0.025 mol% or less.

Note that there are a plurality of definitions from the scientific and industrial viewpoints as to what kind of elements the rare earth element contains.
However, in the present invention, the “rare earth element” is yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium ( Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).
That is, “rare earth element” in this specification does not include scandium (Sc).

In the sintered body for varistors according to the present invention, the production area is limited, there is a concern about stable supply over a long period of time, and there is no need to use rare earth elements that are expensive and have a large fluctuation.
Among the rare earth elements, praseodymium (Pr) and yttrium (Y) have a problem of preventing densification of the sintered body during firing. However, the present invention does not cause such a problem.

-Other rare metals The sintered body for varistors of the present invention is minimized in the amount and type of rare metals other than antimony (Sb) and rare earth elements. RMs other than antimony (Sb) and rare earth elements, that is, lithium (Li), vanadium (V), gallium (Ga), zirconium (Zr), tantalum (Ta), chromium (Cr), germanium (Ge), niobium ( Nb), tellurium (Te), tungsten (W), manganese (Mn), selenium (Se), molybdenum (Mo), cesium (Cs), rhenium (Re), rubidium (Rb), palladium (Pd), barium ( Ba), platinum (Pt), titanium (Ti), nickel (Ni), strontium (Sr), indium (In), hafnium (Hf), and thallium (Tl) content of each metal element is 100 mol. %, It is 0.01 mol% or less, preferably 0.005 mol% or less.

(5) Tin (Sn)
In many conventional sintered bodies for zinc oxide-based varistors, tin (Sn) is intentionally added, for example, in the form of tin oxide and has been actively used. This is presumably because, by using tin (Sn), a liquid phase can be formed during firing, and the resulting sintered body can be densified.
However, as a result of intensive studies, the present inventors have made zinc oxide the main component, bismuth oxide is 0.9 to 1.2 mol% in terms of bismuth (Bi), and cobalt oxide is 1.0 in terms of cobalt (Co). It was found that in a component system containing ˜1.5 mol%, even if tin (Sn) is not added, it can be sufficiently fired within 850 to 950 ° C. and high varistor characteristics can be obtained. On the contrary, it has been found that when 0.5 mol% of tin is added to this composition, although the insulation property is high, the characteristic is deteriorated to a varistor characteristic having a nonlinear constant of 2 or less.

  For this reason, the sintered body for varistors according to the present invention has a tin (Sn) content of zero or less than an impurity level. The general content (impurity level) of tin (Sn) as an impurity is, for example, 0.01 mol% or less, preferably 0.005 mol% or less when the entire metal element is 100 mol%.

(6) Other elements In one of the preferred embodiments of the present invention, the sintered body for varistors of the present invention comprises 0.9 to 1.2 mol% of bismuth oxide in terms of bismuth (Bi) and cobalt (Co). It consists of 1.0 to 1.5 mol% of cobalt oxide in terms of conversion, and the remaining zinc oxide and inevitable impurities.
An example of the level of such inevitable impurities is 0.01 mol% or less per element, and 0.1 mol% or less of the inevitable impurities as a whole.
“Inevitable impurities” usually means impurities that are unintentionally contained during the manufacturing process and handling. However, even if it is intentionally added, if the content is not more than the above-mentioned “impurity level”, the technical effect due to the addition cannot be sufficiently obtained. That is, in this specification, “inevitable impurities” means that the content is below the above “impurity level” regardless of whether it is intentionally added or unintentionally contained. To do. Therefore, in the present invention, as described above, since RM and tin (Sn) are contained only at an impurity level or less, RM and tin (Sn) are included in “inevitable impurities”.

However, the present invention is not limited to this. In another preferred embodiment of the present invention, any element other than RM and tin (Sn) or a compound thereof may be used in order to obtain desired varistor characteristics.
Such elements or compounds may be contained in a total of, for example, 5 mol% or less, preferably 3 mol% or less. If it is about this level, it is possible to ensure sufficient varistor characteristics.

1-2. Characteristics The characteristics of the sintered body for varistors of the present invention obtained by firing at 850 ° C. to 950 ° C. having such a composition are exemplified.
The sintered body for varistors of the present invention has excellent varistor characteristics as described above. Therefore, the varistor characteristics will be described in detail below.
As main varistor characteristics, varistor voltage, insulation resistance and nonlinear resistance are known. These will be described.

-Varistor voltage A varistor (sintered varistor) has a characteristic that its resistance value changes suddenly according to the applied voltage. That is, when the applied voltage exceeds a predetermined level, the electrical resistance rapidly decreases, and the current that has hardly flowed until then suddenly flows out.
The voltage between varistor terminals (applied voltage) when a current of 1 mA flows through the sintered body for varistor is called varistor voltage. Since the varistor voltage depends on the particle size of the varistor (varistor material) and the distance between the electrodes, it can be controlled within a certain range by controlling them. Further, in order to obtain a certain varistor voltage, it is necessary that the nonlinear constant described later is high.
In the sintered body for varistors according to the present invention, the varistor voltage can be controlled in a wide range of 90 to 250 V with respect to the distance between the electrodes of 200 μm by selecting an appropriate composition within the composition range described above.

-Insulation resistance The insulation resistance value means the resistance value at 1/10 of the varistor voltage.
When the insulation resistance value is low, a large amount of current flows and leak current is generated. For this reason, it is considered that the element has an insulation resistance of 10 MΩ or more. And in order to achieve this 10 MΩ reliably, when it has a higher resistance value, the freedom degree of design is high and preferable. In the sintered body for varistors according to the present invention, for example, a high insulation resistance value of 10 GΩ can be obtained.

-Nonlinear constant The nonlinear constant can be obtained by the following equation (1).

Nonlinear constant = log ₁₀ (I1 / I2) / log (V1 / V2) (1)

Here, I1 is 1 mA, V1 is a voltage between varistor terminals when a current of I1 = 1 mA flows, I2 is 0.01 mA, and V2 is a voltage between varistor terminals when a current of I2 = 0.01 mA flows. It is.

  It can be said that when the nonlinear constant is greater than 1, it has a non-linear resistance. The higher this value, the more accurate and preferable the response control is for an abnormal current. Many of the sintered bodies for zinc oxide varistors currently in general use have a non-linear constant of 20 or more, so that it is 20 or more as a guide. In the sintered body for varistors according to the present invention, for example, a nonlinear constant of 20 or more can be obtained.

In order to obtain such excellent varistor characteristics, it is also important to control the grain size of the crystal grains. As described above, in the present invention, it is possible to perform firing at a relatively low temperature of 850 ° C. to 950 ° C. by appropriately selecting the composition.
For this reason, the grain size of the crystal grains can be set to 1 μm to 10 μm, for example.
The particle size can be determined by the intercept method. More specifically, the polishing surface of the sintered body for varistor is thermally etched at a temperature lower than the sintering temperature to clarify the grain boundaries, and then a micrograph at a magnification of 1000 times is obtained. Next, a straight line having a length of 100 μm is drawn on the micrograph, the number of grain boundaries intersecting with the straight line is counted, and the grain size value is obtained by dividing the straight line length (100 μm) by the number of grain boundaries intersecting. This operation is performed a plurality of times, and the average value is calculated to obtain the particle size.

2. Manufacturing method of sintered body for varistor Next, a manufacturing method of the sintered body for varistor described above will be described.
(1) Preparation of mixed raw material (mixed powder) First, a mixed raw material (mixed powder) having substantially the same composition as the sintered body for varistor to be obtained is prepared. Here, “substantially the same composition” means that there is a slight difference in composition between the obtained sintered body for varistors in consideration that some of the components change due to evaporation or the like in the firing step or the like. It means to allow.
Note that the composition of the mixed raw material (mixed powder) is used to promote mixing or to hold the mixed mixed powder in a slurry state, and most of it evaporates in the firing step. For example, ethanol and PVB ( Polyvinyl butyral) and the like, and a plasticizer such as dioctyl phthalate used for maintaining the shape during sheet molding are not included.
From the same point of view, the composition of the mixed raw material (mixed powder) is used to make the mixed raw material into a desired shape such as a sheet, and most of it evaporates in the firing process, organic solvent, plasticizer, binder And no vehicles obtained from these.

  The mixed raw materials are, for example, a raw material such as an oxide such as zinc oxide, bismuth oxide and cobalt oxide, and after weighing these raw materials so as to be substantially the same as the composition of the sintered body for varistors to be obtained, It can be obtained by mixing crude raw materials.

Various known methods may be used for mixing regardless of wet or dry methods.
An example of the mixing method is to use a ball mill. For example, a dispersion material such as ethanol and a raw material weighed together with balls such as zirconia balls may be put into a ball mill container and mixed by ball milling to obtain a mixed material.

Conventionally, heat treatment (calcination) is often performed to obtain a mixed raw material.
For example, in Patent Document 3, when obtaining a mixed raw material, bismuth oxide, antimony oxide, and copper oxide, which are a part of a plurality of types of raw materials used, are premixed and calcined at a temperature of 350 to 750 ° C. The mixed raw material is obtained and fired. Similarly, Patent Documents 4 to 6 disclose that a part (two or more) of a plurality of types of raw materials to be used are mixed in advance and heat-treated at a temperature of 300 ° C. or higher.

These heat treatments are carried out in order to mix a part of the raw materials in advance and diffuse the mutual components so that the composition becomes uniform in the sintered body after firing.
However, in the present invention, the mixed raw material is preferably obtained without performing such heat treatment. Thereby, a manufacturing process becomes simple and it becomes possible to manufacture the sintered compact for varistors at lower cost.
Further, the present inventor obtains a mixed raw material without performing heat treatment in this way, and uses this mixed raw material to perform firing at 850 ° C. to 950 ° C. It was found that the varistor characteristics, in particular the nonlinear constant, of the obtained sintered body for varistors can be improved by 20% or more, compared with the case where firing was carried out.

In the present invention, RM and tin (Sn) are contained only at an impurity level or lower, that is, the essential components are main components of zinc oxide, bismuth oxide, and cobalt oxide. Since components that are easily diffused are mainly used, it is considered that it is not necessary to perform heat treatment before firing, but rather, it is thought to have led to a result that overturned the conventional common sense that superior characteristics can be obtained without heat treatment.
In addition, "heat treatment" as used in this specification means mixing two or more types of raw materials that are a part of a plurality of types of raw materials (powder materials) used to obtain a desired composition, for example, Heating to 300 ° C. or higher, which is a single oxide or the like, heat treatment performed for the purpose of obtaining each raw material, or for the purpose of dehydrating the obtained single raw material Does not include the heat treatment to be performed.

(2) Production of Varistor Laminate Having Sintered Body for Varistor and Electrode Using the obtained mixed raw material, it is molded using any known means, whether dry or wet, and fired under predetermined conditions. Thus, a sintered body may be obtained.
For example, the mixed raw material may be used in a dry state to obtain a molded body (a green compact), and the molded body may be fired to obtain a sintered body.
Alternatively, a slurry obtained by dispersing the mixed raw material in an organic dispersion medium such as ethanol or an inorganic dispersion medium (slurry mixed raw material or paste) may be obtained and fired to obtain a sintered body.
In addition, after mixing and mixing the mixed raw materials in a vehicle obtained by mixing an organic solvent, a plasticizer and a binder, the mixture is heated to about 100 ° C. or less while performing vacuum defoaming, etc. A mixed raw material molded body having an arbitrary shape may be obtained, and these may be laminated as necessary, and fired to obtain a sintered body.

  FIG. 1 is a schematic perspective view illustrating a method of obtaining a sintered body using a slurry-like mixed raw material. 1A shows a method for obtaining a mixed raw material sheet from a slurry, FIG. 1B shows a state in which the mixed raw material sheet is punched into a desired shape, and FIG. 1C shows a punched mixed raw material sheet. Is shown, and the electrode material is disposed. 1A to 1C, when there are a plurality of figures having the same figure but different signs (parts such as “(a)”) after the numerals, these are collectively referred to as “FIG. And may be called by the numbers in the figure.

The method illustrated in FIG. 1 will be described below.
After adding a dispersion medium and, if necessary, PVB and / or a plasticizer to the mixed raw material to obtain a slurry (mixed raw material slurry), as shown in FIG. The mixed raw material sheet 2 can be obtained on the resin film 8 by applying to the resin film 8 and drying.
By punching this along the line A in FIG. 1A, as shown in FIG. 1B, the mixed raw material sheet 2 on the resin sheet 8 has a predetermined shape (disk shape in FIG. 1B). Can be.

The mixed raw material sheet 2 is peeled from the resin film 8 and, as shown in FIG. 1 (c), a plurality (three in FIG. 1 (c)) of mixed raw material sheets 2 are laminated, and the mixed raw material sheet laminate 22 is formed. Form. Then, the first electrode sheet 6A (for example, a silver (Ag) electrode sheet) is laminated on the lower surface of the mixed raw material sheet laminate 22, and the second electrode sheet 6B (silver (Ag)) is laminated on the upper surface of the mixed raw material sheet laminate 22. ) Electrode sheet).
Thereafter, the first electrode sheet 6A (electrode sheet 6) and the second electrode sheet 6B (electrode sheet 6) are pressed so as not to be short-circuited, and between the mixed raw material sheets 2 and the mixed raw material sheet 2 and the first. Between the electrode sheet 6A and the mixed raw material sheet 2 and the second electrode sheet 6B. The pressing is preferably performed by heating to 100 ° C. or lower.

Then, the mixed material sheet laminate 22 in which the first electrode sheet 6A is disposed on the lower surface and the second electrode sheet 6B is disposed on the upper surface is fired.
Firing is performed at a firing temperature of 850 ° C to 950 ° C.
Firing may be performed in air, or may be performed in an oxygen atmosphere as necessary.

By performing such firing, the varistor laminated body 22 (sintered body) having the first electrode 6A (for example, silver electrode) on the lower surface and the second electrode 6B (for example, silver electrode) on the upper surface. ) Can be obtained.
In the embodiment shown in FIG. 1, a plurality of mixed raw material sheets 2 are laminated, but instead, the first electrode sheet 6 </ b> A on the lower surface of one mixed raw material sheet 2 and the second electrode sheet 6 </ b> B on the upper surface. May be formed and fired to obtain a sintered body.

3. Multilayer substrate and manufacturing method thereof (1) Multilayer substrate (basic structure of varistor-embedded multilayer substrate) and manufacturing method thereof Multilayer substrate (basic structure of varistor-embedded multilayer substrate) as an example of the use of the above-described varistor sintered body Will be described.
2A is a perspective view showing a multilayer substrate 100 as a basic structure of the multilayer substrate of the present invention, and FIG. 2B is a sectional view showing a XIVb-XIVb cross section of FIG. 2A. .
The multilayer substrate 100 includes a first insulating layer 10A (insulating layer 10), a second insulating layer 10B (insulating layer 10), a third insulating layer 10A in order (in order from the top in the embodiment shown in FIG. 2A). The insulating layer 10C (insulating layer) is laminated. The varistor layer 2 is disposed inside the second insulating layer 10B. In the embodiment shown in FIG. 2B, the varistor layer 2 is disposed inside the through hole that penetrates the second insulating layer 10B.

Internal electrodes 6 </ b> C are disposed on the upper and lower surfaces of the varistor layer 2.
The internal electrode 6C disposed on the upper surface of the varistor layer 2 is connected to the through electrode 6D penetrating the first insulating layer 10A to form the electrode 6. By this electrode 6, the upper surface of the first insulating layer 10A (the portion exposed from the upper surface of the first insulating layer 10A of the through electrode 6D) and the varistor layer 2 can be electrically connected.
Similarly, the internal electrode 6C disposed on the lower surface of the varistor layer 2 is connected to the through electrode 6D penetrating the third insulating layer 10C to form the electrode 6. With this electrode 6, the lower surface of the third insulating layer 10C (the portion exposed from the lower surface of the third insulating layer 10C of the through electrode 6D) and the varistor layer 2 can be electrically connected.
The two internal electrodes 6C are opposed to each other, and the varistor layer 2 is disposed therebetween. With this configuration, when an abnormally high voltage (high current) is generated between the two internal electrodes 6C due to noise or the like, a current flows through the varistor layer 2. By using this basic structure to form a multi-layered substrate structure such as an interposer, almost no current flows through the device to be protected, such as a semiconductor chip, when an abnormally high voltage occurs, so that these devices can be protected Can do. In addition, by applying a basic structure in which a varistor layer is partially embedded in an insulating layer, such as the multilayer substrate 100, for high-speed communication modules, interposers, etc., the electrical wiring formed by the electrodes is arranged almost in the insulating layer. Therefore, it is possible to realize a multi-layer substrate utilizing the excellent transmission characteristics of the insulating layer.

Next, a method for manufacturing the multilayer substrate 100 will be described.
FIG. 3A to FIG. 3D are perspective views showing a method for manufacturing the laminate 150. First, the laminated body 150 is produced.
As shown in FIG. 3A, an insulating sheet 10 to be an insulating layer is prepared by firing, and then a through hole 14 is formed in the insulating sheet 10 as shown in FIG. The insulating sheet 10 is, for example, a slurry obtained by mixing a mixed raw material for an insulating sheet with a binder, applied onto a resin sheet by a doctor blade method using a sheet molding machine and dried, and then peeled off the resin sheet. Or the like.
By filling the through hole 14 of the insulating sheet 10 with a silver electrode paste and drying it, an electrode paste layer 6D that becomes the through electrode 6D after firing is formed.
Next, as shown in FIG. 3 (d), the electrode paste is applied to the upper surface of the insulating sheet 10 by a method such as applying a silver electrode paste to the surface of the insulating sheet 10 using a screen printing method and then drying it. An electrode paste layer 6C is formed so as to be in contact with the layer 6D.
Thereby, the laminated body 150 can be obtained. Two stacked bodies 150 are produced.

Next, the stacked body 160 is formed. FIG. 4 is a perspective view showing the laminate 160. The laminate 160 is obtained by covering the surface (at least the main surface) of the electrode paste layer 6 </ b> C of the laminate 150 with the varistor slurry layer 2.
Using one of the two stacked bodies 150, the stacked body 160 can be formed by the following method.
The raw materials are mixed with a ball mill or the like, then dried and crushed to obtain a mixed raw material (mixed dry powder) having the above-mentioned predetermined components. A mixed raw material slurry in which the mixed raw material is dispersed in an organic dispersion medium (vehicle) such as ethanol or an inorganic dispersion medium is obtained.
Of the exposed surface of the electrode paste layer 6C of the laminate 150, at least the main surface is covered with the obtained mixed raw material slurry using a method such as screen printing, and then dried, thereby drying the insulating sheet 2 and the through electrode. A laminate 160 having 6D, the electrode paste layer 6C, and the varistor slurry layer 2 can be obtained.

FIG. 5 is a diagram illustrating a method for manufacturing the multilayer substrate 100.
The press process for obtaining a composite laminated body is demonstrated using FIG.
In order from the top, the laminate 160 (electrode paste layer 6C is not shown) arranged so that the varistor slurry layer 2 is on the lower surface side, and the varistor slurry layer 2 of the laminate 160 and the electrode paste layer 6C of the laminate 150 are accommodated. As shown in FIG. 5, the insulating sheet 10 having the possible through holes 14A and the laminated body 150 arranged so that the electrode paste layer 6C is on the upper surface side are combined with the varistor slurry layer 2, the through holes 14A, and the electrode paste layer 6C. And align them.
Then, the insulating sheet 10 of each of the laminates 150 and 160 is brought into contact with the insulating sheet 10 having the through holes 14A, whereby the electrode paste layer 6C and the varistor slurry layer 2 of the laminate 160 and the electrode paste layer of the laminate 150 are obtained. 6C is stacked in the through hole 14A.
By pressing in this state, a composite laminate can be obtained.

  The obtained composite laminate is fired at a temperature between 850 ° C. and 950 ° C. Thereby, the multilayer substrate 100 can be obtained.

(2) Multilayer substrate (modified example of basic structure of multilayer substrate with built-in varistor) and manufacturing method thereof FIG. 6A is a perspective view showing a multilayer substrate 200 according to the modified example, and FIG. It is sectional drawing which shows the XVIIIb-XVIIIb cross section of 6 (a).
The multilayer substrate 200 has a configuration similar to that of the multilayer substrate 100. That is, the multilayer substrate 200 includes a first insulating layer 10A (insulating layer 10), a second insulating layer 10B (insulating layer 10), and a first layer in order (in the embodiment shown in FIG. 3 insulating layers 10C (insulating layer 10). The varistor layer 2 is disposed inside the second insulating layer 10B. In the embodiment shown in FIG. 6B, the varistor layer 2 is disposed inside the through hole that penetrates the second insulating layer 10B.

  In the multilayer substrate 100, the varistor layer 2 is formed by firing the varistor slurry layer 2. In the multilayer substrate 200, the varistor layer 2 is formed using the mixed raw material sheet 2 shown in FIG. Since the mixed raw material sheet 2 is usually more rigid than the varistor slurry layer 2, there is little deformation in the pressing process. For this reason, the variation in the thickness in the obtained varistor layer 2 is small, and in particular, there is an advantage that the difference in thickness between the central portion and the end portion is small.

  Note that the method of manufacturing the multilayer substrate 200 replaces the surface (at least the main surface) of the electrode paste layer 6D with the varistor slurry layer 2 when forming the laminated body 160, and replaces the surface (at least the surface of the electrode paste layer 6D). The same manufacturing method as that of the laminate 100 may be used except that the mixed raw material sheet 2 is disposed so as to cover the main surface).

  2 to 6, the example in which the two internal electrodes 6C are respectively disposed on the upper surface and the lower surface of the varistor layer 2 has been described. However, the two internal electrodes 6C have the same main surface ( The upper surface or the lower surface may be spaced apart from each other. That is, the internal electrodes 6 </ b> C only need to be spaced apart from each other on any main surface of the varistor layer 2.

1. Example 1
The raw materials shown in Table 1 were weighed so as to have the composition shown in the same table, put into a ball mill container together with ethanol and zirconia balls, and ball mill mixed at 100 rpm for 20 hours. The composition in this example is shown in mol% in terms of metal element. That is, the molar ratio was calculated and determined in consideration of only the metal atom bonded to oxygen without considering the oxygen atom contained in each oxide. In Table 1, Zn, Bi, Co, The mol% of each metal element of Mn and Cr is shown.
Further, all samples (mixed raw materials after drying) shown in Table 1 were subjected to ICP (inductively coupled plasma) wet analysis. As a result, RM and tin (Sn) were both below the detection limit (detection limit: 100 ppm by mass ratio). This means that each content of RM and tin (Sn) obtained by converting from mass ratio to molar ratio is less than 0.01 mol%.

The obtained mixed raw material was taken out and dried, and then mixed with ethanol, PVB and a plasticizer to prepare a slurry mixed raw material. At this time, the content of PVB in the slurry was 10% by volume.
Using this slurry-like mixed raw material, a varistor laminate was obtained by the method shown in FIG.
Specifically, the slurry-like mixed raw material was applied on the PET film 8 with a thickness of 0.07 mm, and then dried to obtain the mixed raw material sheet 2.
Similarly, silver (Ag) powder is mixed with ethanol, PVB (polyvinyl butyral) and a plasticizer to prepare a slurry. The slurry is applied to a thickness of 0.08 mm on a PET film, and then dried to obtain a silver electrode sheet. 6 was obtained.

After the PET film 8 coated with the slurry was punched out, the PET film 8 was peeled off to obtain a disk-shaped mixed raw material sheet 2 (diameter 14 mm × thickness 0.07 mm). Three mixed raw material sheets 2 were laminated to obtain a mixed raw material sheet laminate 22.
A silver electrode sheet 6 (diameter 6 mm × thickness 0.05 mm) was laminated on both surfaces of the mixed raw material sheet laminate to form an electrode, which was pressed and pressed at 85 ° C. so as not to short-circuit the electrode.

  The mixed raw material sheet laminate 22 provided with the silver electrodes 6 on both sides was heated at a rate of temperature increase of 200 ° C./hour and fired at 900 ° C. for 2 hours to obtain a varistor laminate 22.

For the samples 1 to 11 of the varistor laminate 22, the current flowing between the electrodes was measured using an insulation resistance meter R8340 manufactured by Advantest Corporation, and the varistor characteristics (insulation resistance value, Nonlinear constant, varistor voltage). The insulation resistance value is a resistance value at 1/10 of the varistor voltage. The nonlinear constant was obtained by the above equation (1).
The results are shown in Table 2.

From Table 2, Samples 3 to 6 which are examples according to the present invention have better varistor characteristics than Samples 1, 2 and 7 to 11 which are comparative examples, and particularly high nonlinearity of 20 or more. A constant is obtained.
When composition analysis of the structures of Samples 3 to 6 was performed by EDX (energy dispersive X-ray spectroscopy), it was confirmed that cobalt was dissolved in the zinc oxide particles. As described above, solid solution cobalt is expected to be a donor that emits electrons, and Samples 3 to 6 affect the formation of double Schottky barriers related to the varistor characteristics of zinc oxide varistors. Since the balance between the electron density trapped at the grain boundary level and the ionized donor density in the grain became suitable, it is assumed that such a high nonlinear constant was obtained. In contrast, Samples 1 and 2 in which the addition amount of cobalt oxide is less than the range of the present invention, Sample 7 in which the addition amount of cobalt oxide is greater than the range of the present invention, and Sample 8 in which the addition amount of bismuth oxide is less than the range of the present invention. The sample 9 in which the amount of bismuth oxide added is larger than the range of the present invention is considered to have a low nonlinear constant because this balance was not suitable. In Samples 10 and 11, the reason is unknown due to the addition of manganese and chromium, but it is presumed that the characteristics of the grain boundaries are not preferable.

2: Varistor layer (mixed raw material sheet or paste layer before firing)
6: Electrode 6A: 1st electrode 6B: 2nd electrode 6C: 1st internal electrode 6D: 2nd internal electrode 8: Resin film 10: Insulating layer 10A: 1st insulating layer 10B: 2nd insulation Layer 10C: Third insulating layer 22: Varistor laminated body (mixed raw material sheet laminated body before firing)

Claims (5)

Mainly zinc oxide,
Bismuth oxide is contained in 0.9 to 1.2 mol% in terms of bismuth (Bi), cobalt oxide is contained in 1.0 to 1.5 mol% in terms of cobalt (Co),
RM (RM is antimony (Sb), rare earth element, lithium (Li), vanadium (V), gallium (Ga), zirconium (Zr), tantalum (Ta), chromium (Cr), germanium (Ge), niobium ( Nb), tellurium (Te), tungsten (W), manganese (Mn), selenium (Se), molybdenum (Mo), cesium (Cs), rhenium (Re), rubidium (Rb), palladium (Pd), barium ( Ba), platinum (Pt), titanium (Ti), nickel (Ni), strontium (Sr), indium (In), hafnium (Hf), thallium (Tl)) and tin (Sn) content are below the impurity level A sintered body for a varistor, characterized in that   In order, the 1st insulating layer, the varistor layer which is the sintered compact for varistors of Claim 1, a 2nd insulating layer, the 1st internal electrode arrange | positioned on the main surface of the said varistor layer, and 1st And a plurality of internal electrodes. A first insulating layer, a second insulating layer, and a third insulating layer, which are sequentially stacked;
The second insulating layer includes therein a varistor layer that is a sintered body for varistors according to claim 1,
A multilayer substrate comprising a first internal electrode and a second internal electrode arranged on a main surface of the varistor layer. 1) At least zinc oxide, bismuth oxide, and cobalt oxide are mixed without heat treatment, zinc oxide is the main component, and bismuth oxide is 0.9 to 1.2 mol% in terms of bismuth (Bi), Cobalt oxide is contained in an amount of 1.0 to 1.5 mol% in terms of cobalt (Co), and RM (RM is antimony (Sb), rare earth element, lithium (Li), vanadium (V), gallium (Ga), zirconium (Zr ), Tantalum (Ta), chromium (Cr), germanium (Ge), niobium (Nb), tellurium (Te), tungsten (W), manganese (Mn), selenium (Se), molybdenum (Mo), cesium (Cs) ), Rhenium (Re), rubidium (Rb), palladium (Pd), barium (Ba), platinum (Pt), titanium (Ti), nickel (Ni), strike Nchiumu (Sr), and obtaining indium (In), hafnium (Hf), thallium (Tl)) and mixed raw material content is less impurity levels of tin (Sn),
2) A step of firing the mixed raw material at 850 ° C. to 950 ° C .;
The manufacturing method of the sintered compact for varistors characterized by including these. 1) At least zinc oxide, bismuth oxide, and cobalt oxide are mixed without heat treatment, zinc oxide is the main component, and bismuth oxide is 0.9 to 1.2 mol% in terms of bismuth (Bi), Cobalt oxide is contained in an amount of 1.0 to 1.5 mol% in terms of cobalt (Co), and RM (RM is antimony (Sb), rare earth element, lithium (Li), vanadium (V), gallium (Ga), zirconium (Zr ), Tantalum (Ta), chromium (Cr), germanium (Ge), niobium (Nb), tellurium (Te), tungsten (W), manganese (Mn), selenium (Se), molybdenum (Mo), cesium (Cs) ), Rhenium (Re), rubidium (Rb), palladium (Pd), barium (Ba), platinum (Pt), titanium (Ti), nickel (Ni), strike Nchiumu (Sr), and obtaining indium (In), hafnium (Hf), thallium (Tl)) and mixed raw material content is less impurity levels of tin (Sn),
2) disposing a first electrode material on a first insulating sheet made of an insulating material;
3) forming a mixed raw material sheet containing the mixed raw material on the first electrode material;
4) A step of disposing a second electrode material on the mixed raw material sheet;
5) forming a second insulating sheet made of an insulating material on the second electrode material;
6) firing the first insulating sheet, the mixed raw material sheet, and the second insulating sheet at 850 ° C. to 950 ° C .;
A method for producing a multilayer substrate, comprising: