KR101968992B1

KR101968992B1 - Varistor ceramic and the preparing method thereof

Info

Publication number: KR101968992B1
Application number: KR1020150062712A
Authority: KR
Inventors: 이승철; 강승진
Original assignee: 주식회사 아모텍
Priority date: 2015-05-04
Filing date: 2015-05-04
Publication date: 2019-04-15
Also published as: WO2016178537A2; KR20160130653A; WO2016178537A3

Abstract

The present invention relates to a varistor ceramic and a method of manufacturing the same. More particularly, the present invention relates to a varistor ceramic comprising a praseodymium-based zinc oxide and barium titanate (BaTiO ₃ ), wherein the atomic percentage of barium titanate to the praseodymia- A varistor ceramic having improved ESD resistance, excellent electrostatic capacity, and stability during heterojunction, and a method for producing the varistor ceramic.

Description

[0001] Varistor ceramics and their preparation [0002]

The modern information technology (IT) industry is advancing day by day due to the development of the semiconductor industry. Electricity, electronics, and information communication devices use electronic information communication devices which are highly integrated, , And are becoming increasingly sophisticated in pursuit of versatility.

However, the high integration of electronic information communication devices causes the possibility of reacting more sensitively in transient situations, which can be a weak point in securing the reliability of the entire system. These transients can be caused by lightning or lightning, nuclear electromagnetic waves, high energy switching or electrostatic discharge (ESD), among which the most important consideration for electronic circuit protection is electrostatic discharge (ESD) There are two types of inductive loads. For this reason, various methods for protecting the electronic circuit from the transient state have been developed in accordance with the high integration of the electronic information communication device. The optimum method in terms of performance and economy is the use of the surge protection device.

Among them, zinc oxide varistor (ZnO Varistor) is a surge protection element that protects a protected device by discharging abnormal voltage, current, and energy from the front end of the protected device including an electronic device, ie, surge to ground. Or is modularized and widely used throughout the industry. The zinc oxide varistor, which is a polycrystalline ceramics, is characterized in that the grain boundary of the zinc oxide crystal grains is selectively converted to insulation or conductivity depending on the applied voltage to exhibit nonlinear voltage-current characteristics (nonlinear electrical behavior) .

In other words, a zinc oxide varistor is a nonlinear resistor whose resistance changes according to a voltage, and is connected in parallel with a protected device, and operates as an insulator exhibiting high impedance at normal times. By discharging high energy, the protected group is protected.

Zinc oxide varistors prepared by adding a nonlinearity-inducing oxide and a property improving oxide to zinc oxide, which occupy most of the ceramics, are classified into various types according to the types of nonlinearity-induced oxides, and the most common ones are bismuth (Bi ) System, followed by the praseodymium (Pr) system.

ZnO-based varistors formed of ZnO-Bi-based materials or ZnO-Pr-based materials among the material composition systems of varistors are superior in voltage nonlinearity and good in serge current capacity to SiC-based varistors and BaTiO 3 -based varistors, Has been widely used as a material for surge protection devices.

However, the ZnO-Bi-based varistors _{Bi 2 O 3, Sb 2 O} 3, Mn, Co, Ni, Cr, glass frit, consists of a component such as Al, K, the Bi ₂ O component ESD (Electro- Static Discharge resistance is weak, ZnO-Bi varistors including the varistors have a disadvantage in that their ESD characteristics are poor. In addition, since the Sb2O3 component is classified as a carcinogen and its concentration is regulated, the ZnO-Bi varistor containing the Sb2O3 component has disadvantages that it is not free to manufacture. In addition, the ZnO-Pr varistor has a good voltage nonlinearity, but has a drawback that the leakage current is larger than that of the ZnO-Bi varistor. Since the ZnO-Pr varistor contains a Pr component as a raw material of the noble metal series, (Pd or the like) is used in a large amount, resulting in a disadvantage that the manufacturing cost is high.

On the other hand, high-density mounting is rapidly proceeding due to miniaturization and miniaturization of surface mount devices (SMDs) of electronic components in accordance with the tendency of thinning and high functioning of electronic devices in recent years. Since the signal speed of the circuit in the SMD electronic product is several hundred MHz to several GHz, it is necessary to considerably lower the capacitance of the varistor in order to prevent signal delay at such a high signal speed.

Since ZnO varistors have a high relative dielectric constant of several hundreds, the electrode area must be considerably reduced in order to have a small capacitance. However, if the electrode area is reduced to have a small capacitance, the surge resistance is reduced, and the varistor manufacturing process becomes quite complicated. Therefore, there is a need for a ZnO-type varistor having a low dielectric constant.

The present invention relates to a varistor ceramic and a method of manufacturing the varistor ceramic which can improve the ESD resistance by mixing the praseodymia-based zinc oxide and barium titanate (BaTiO ₃ ) in an appropriate ratio, exhibit excellent electrostatic capacity, .

Accordingly, the present invention is characterized in that it comprises a praseodymia-based zinc oxide and barium titanate (BaTiO ₃ ), and has an atomic percentage ratio of barium titanate to praseodymia-based zinc oxide of 88 to 99: 1 to 12 Provides varistor ceramics.

In one preferred embodiment of the present invention, the praseodymium-based zinc oxide comprises ZnO, Pr ₆ O ₁₁ , Co ₃ O ₄ and Nd ₂ O ₃ , and the total weight of the praseodymium- , 90 to 92% by weight of ZnO, ₅ % by weight of Pr ₆ O ₁₁ 0.3 to 0.5 wt%, Co ₃ O ₄ 2 to 3 wt%, and Nd ₂ O ₃ 0.3 to 0.5 wt%.

In a preferred embodiment of the present invention, the varistor ceramics may be sintered at 1300 to 1400 ° C.

In a preferred embodiment of the present invention, the varistor ceramic may have a breakdown voltage of 100 to 800 V at 1 mA as measured by a curve tracer.

In one preferred embodiment of the present invention, the capacitance of the varistor ceramic at 1 kHz is 50 to 400 pF and the relative dielectric constant is 500 to 3000.

In a preferred embodiment of the present invention, the varistor ceramics may have a capacitance of 50 to 300 pF at 1 MHz and a relative dielectric constant of 500 to 2500.

Another aspect of the present invention provides a thin film comprising the varistor ceramic described above.

In a preferred embodiment of the present invention, the thin film may be hetero-bonded to the capacitor layer.

The present invention relates to a process for preparing a mixture comprising mixing praseodymia-based zinc oxide and barium titanate (BaTiO ₃ ) in an atomic ratio of 88 to 99: 1 to 12; Crushing and filtering the mixture and drying it; 3) pulverizing and filtering the dried mixture to obtain powder; Adding powdered PVB (polyvinyl butyral) powder to the pulverized mixture and granulating it; And 5) sintering the granulated mixture by press molding. [5] The present invention also provides a method of manufacturing a varistor ceramic.

In a preferred embodiment of the present invention, drying in step 2 may be performed at 70 ° C to 90 ° C for 1 to 3 hours.

In a preferred embodiment of the present invention, PVB (polyvinyl butyral) powder may be mixed at 5 to 10 wt% with respect to the powder mixture in the third step.

In a preferred embodiment of the present invention, the sintering in the step 5 may be performed at 1300 to 1400 ° C.

1 is an image showing a mold of a varistor ceramic according to the present invention.
2 is an image of a surface of a varistor ceramic produced by sintering at 1200 ° C.
FIG. 3 is an image of a broken section of a varistor ceramic produced by sintering at 1200 ° C.
4 is an image of a surface of a varistor ceramic produced by sintering at 1350 ° C.
5 is an image of a fracture surface of a varistor ceramic manufactured by sintering at 1350 ° C.
6 is a graph showing breakdown voltages of Comparative Examples 3 to 6.
7 is a graph showing breakdown voltages of Examples 1 to 3 and Comparative Example 1. Fig.
8 is a graph showing the relative dielectric constants of Comparative Examples 3 to 6.

The present invention relates to a varistor ceramic comprising a praseodymia-based zinc oxide and barium titanate (BaTiO ₃ ) and having an atomic percentage ratio of barium titanate to praseodymia-based zinc oxide of 88 to 99: . Hereinafter, the present invention will be described in more detail.

The varistor ceramics according to the present invention have an effect of improving ESD (electrostatic discharge) resistance, excellent electrostatic capacity, and stability at the time of heterojunction when they are mixed in the above ratio.

At this time, the atomic percentage ratio of barium titanate to praseodymium-based zinc oxide is preferably 88 to 99: 1 to 12, more preferably 90 to 96: 4 to 10. When the atomic percentage ratio of the barium titanate to the praseodymium-based zinc oxide is less than 99: 1, there is a problem that the relative dielectric constant and the breakdown voltage of the varistor ceramics produced are not significantly different from each other. When the ratio exceeds 88:12 The sintering ability is lowered and the sintered density is not more than a certain level.

At this time, the praseodymia-based zinc oxide can be used as long as it can be generally purchased or manufactured, and it is not particularly limited, but preferably contains ZnO, Pr ₆ O ₁₁ , Co ₃ O ₄ and Nd ₂ O ₃ , based on the total weight of the zinc oxide-based infrastructure lost three audio ZnO 90 ~ 92% by weight, Pr ₆ O ₁₁ 0.3 to 0.5 wt%, Co ₃ O ₄ 2 to 3 wt%, and Nd ₂ O ₃ 0.3 to 0.5 wt%.

In the varistor ceramics according to the present invention, the varistor ceramics may be sintered at 1300 to 1400 ° C. There is a problem that varistor characteristics are lost when the varistor ceramics are sintered at a temperature lower than 1300 DEG C and there is a problem that the function of the varistor is lowered and the leakage current is increased when the varistor ceramic is sintered at a temperature exceeding 1400 DEG C .

In the varistor ceramics according to the present invention, the varistor ceramics may have a breakdown voltage of 100 to 800 V at 1 mA, preferably 1 to 500 V, at a breakdown voltage of 1 mA, as measured by a curve tracer Lt; / RTI >

In addition, the varistor ceramics may have a capacitance of 50 to 400 pF at 1 kHz, a relative dielectric constant of 500 to 3000, a capacitance at 1 MHz of 50 to 300 pF, and a relative dielectric constant of 500 to 2500.

The varistor ceramics according to the present invention can exhibit the above physical properties and can be manufactured to exhibit a wide range of voltage and electrostatic capacity. In addition, by applying a relatively simple addition method, it is possible to artificially control various electrical characteristics based on the same composition.

The present invention also provides a thin film comprising the above varistor ceramics. The thin film may be heterogeneously bonded to the capacitor layer and disposed at a proper position in accordance with a desired characteristic, so that the relative dielectric constant and the voltage can be adjusted so that desired characteristics can be realized.

The present invention also relates to a method for producing a mixture comprising: a first step of mixing a praseodymium-based zinc oxide and barium titanate (BaTiO ₃ ) in an atomic ratio of 88 to 99: 1 to 12 to prepare a mixture; Crushing and filtering the mixture and drying it; 3) pulverizing and filtering the dried mixture to obtain powder; Adding powdered PVB (polyvinyl butyral) powder to the pulverized mixture and granulating it; And 5) sintering the granulated mixture by press molding. [5] The present invention also provides a method of manufacturing a varistor ceramic. Hereinafter, the present invention will be described in more detail by step.

In the method of manufacturing the varistor ceramics according to the present invention, the first step is a step of mixing the praseodymia-based zinc oxide and barium titanate (BaTiO ₃ ) in an atomic ratio of 88 to 99: 1 to 12 to prepare a mixture In the above mixture, the atomic percentage ratio of barium titanate to praseodymia-based zinc oxide is preferably 88 to 99: 1 to 12, more preferably 90 to 96: 4 to 10. When the atomic percentage ratio of the barium titanate to the praseodymium-based zinc oxide is less than 99: 1, there is a problem that the relative dielectric constant and the breakdown voltage of the varistor ceramics produced are not significantly different from each other. When the ratio exceeds 88:12 The sintering ability is lowered and the sintered density is not more than a certain level.

The praseodymia-based zinc oxide can be used as long as it can be generally purchased or manufactured, and is not particularly limited, but preferably includes ZnO, Pr ₆ O ₁₁ , Co ₃ O ₄ and Nd ₂ O ₃ , based on the total weight of the zinc oxide-based infrastructure lost three audio ZnO 90 ~ 92% by weight, Pr ₆ O ₁₁ 0.3 to 0.5 wt%, Co ₃ O ₄ 2 to 3 wt%, and Nd ₂ O ₃ 0.3 to 0.5 wt%.

In the method for producing varistor ceramics according to the present invention, the step 2 is a step of pulverizing, filtering and drying the mixture, and the mixture may be pulverized by milling to pulverize the mixture. At this time, the drying in step 2 is preferably performed at 70 ° C to 90 ° C for 1 to 3 hours, more preferably at 80 ° C to 90 ° C for 2 to 3 hours.

In the method of manufacturing varistor ceramics according to the present invention, the step 3 is a step of pulverizing and drying the dried mixture to powder, the pulverization can be carried out through a mortar, and the filtration is carried out through a standard net .

In the method of manufacturing varistor ceramics according to the present invention, the step 4 is a step of adding PVB (polyvinyl butyral) powder to the powdered mixture and granulating the blended mixture, wherein PVB (polyvinyl butyral) powder in an amount of 5 to 10% by weight, preferably 5 to 8% by weight. The PVB is introduced for the purpose of maintaining the desired shape and securing the adhesion between the respective raw materials when uniaxial pressing is performed. When the PVB is introduced at less than 5% by weight, there is a problem in the edge portion after uniaxial pressing, There is a problem that it is difficult to detach from the molding mold due to excessive adhesive force and the sintering property is deteriorated due to an excessive volume increase.

In the method of manufacturing varistor ceramics according to the present invention, the step 5 is a step of pressing and sintering the granulated mixture, and the electrical characteristics of the varistor ceramics according to the present invention can be controlled through the sintering temperature . The sintering in step 5 may be performed at 1300 to 1400 ° C, preferably at 1350 to 1400 ° C.

Hereinafter, the present invention will be described in more detail with reference to the following examples. The following examples are provided to illustrate the present invention, but the scope of the present invention is not limited by the following examples.

[ Example ]

Example One. Varistor Manufacture of ceramic

(1) The mixture was mixed with ZnO (90 to 92%), Pr6O11 (0.3 to 0.5%), Co3O4 (2 to 3%) and Nd2O3 (0.3 to 0.5%), calcined at 800 ° C. for 2 hours, Mica based zinc oxide and perovskite oxide, barium titanate (BaTiO ₃ ), were mixed in a 250 ml capacity plastic bottle at an atomic ratio of 97: 3.

(2) ZrO ₂ balls were introduced into the mixture, followed by ball milling at a speed of 250 rpm for 24 hours on a milling machine (M / C). The mixture was recovered by ball milling, filtered and sieved through a 200-mesh sieve. The filtered slurry was dried in an electric oven at 80 ° C for 2 hours.

(3) The dried powder was pulverized using a mortar and filtered using a standard netting (ASTM mesh No.500 = 25 mu m).

(4) 6% by weight of PVB was mixed with the mixture and granulated using a plastic spatula and a standard mesh (ASTM mesh No. 325 = 45 μm).

(5) The granules were weighed into a molding die having a diameter of 8.5, and then subjected to uniaxial pressing by applying a pressure of 1000 kg / cm < 3 >. After completion of the molding, the thickness was measured and charged into a sintering furnace, which was sintered at 1350 ° C for 4 hours to prepare a varistor ceramic.

Example 2. Varistor Manufacture of ceramic

Varistor ceramics were prepared in the same manner as in Example 1 except that praseodymia-based zinc oxide and barium titanate were mixed in an atomic ratio of 95: 5.

Comparative Example One. Varistor Manufacture of ceramic

Varistor ceramics were prepared in the same manner as in Example 1 except that only praseodymium based zinc oxide was used.

Example 3: Preparation of varistor ceramics

Varistor ceramics were prepared in the same manner as in Example 1 except that praseodymia-based zinc oxide and barium titanate were mixed in an atomic ratio of 90:10.

Comparative Example 3. Varistor Manufacture of ceramic

Varistor ceramics were prepared in the same manner as in Example 1, except that only praseodymium-based zinc oxide was used and sintered at 1200 ° C.

Comparative Example 4. Varistor Manufacture of ceramic

Varistor ceramics were prepared in the same manner as in Example 1 except that praseodymia-based zinc oxide and barium titanate were mixed at an atomic ratio of 97: 3 and sintered at 1200 ° C.

Comparative Example 5. Varistor Manufacture of ceramic

Varistor ceramics were prepared in the same manner as in Example 1 except that praseodymia-based zinc oxide and barium titanate were mixed at an atomic ratio of 95: 5 and sintered at 1200 ° C.

Comparative Example 6. Varistor Manufacture of ceramic

Varistor ceramics were prepared in the same manner as in Example 1 except that praseodymia-based zinc oxide and barium titanate were mixed at an atomic ratio of 90:10 and sintered at 1200 ° C.

[ Experimental Example ]

Experimental Example One. Varistor Electrical Characteristic Analysis of Ceramic

The thickness and diameter of the varistor ceramics prepared in Examples 1 to 3 and Comparative Example 1 and Comparative Examples 3 to 6 were measured, and then the density was measured. The electrodes were printed on the front and back surfaces of the varistor ceramics, and then the electrode was baked. When the electrode had been completely baked, it was recovered and the breakdown voltage, leakage current, and dielectric characteristics were measured using a programmable curve tracer (Tektronix 370B) Were measured. The results are shown in Table 1 below. The breakdown voltages of the following Examples 1 to 2 and Comparative Examples 1 to 6 are shown in FIG. 6 and FIG. 7, and the relative dielectric constant is shown in FIG.

At this time, the breakdown voltage indicated as not measurable indicates that the measurement limit voltage of the curve tracer exceeds 2000 V.

Pr-Zn: BaTiO ₃ density
(g / cm3) Vn V / mm IL Cp
(pF @ 1 kHz) Relative dielectric constant Cp
(pF @ 1 MHz) Relative dielectric constant Comparative Example 1 100: 0 5.27 59 52 38.04 1195.9 9269.75 476 3713.38 Comparative Example 3 100: 0 5.24 1093 1066 0.12 23.54 164.09 13.34 93

According to Examples 1 to 3, in which the atomic percentage ratio of barium titanate to praseodymium-based zinc oxide is in the range of 88 to 99: 1 to 12, the breakdown voltage is 100 to 800 V . &Lt; / RTI > However, in the case of Comparative Example 1, as can be seen from FIG. 7 and Table 1, it can be seen that the breakdown voltage is 59 V at 1 mA, which is a remarkably low value of 100 V or less.

6, Comparative Examples 3 and 6 were varistor ceramics produced by sintering at 1200 DEG C, Comparative Example 5 and Comparative Example 6 showed that the breakdown voltage exceeded 2000 V at 1 mA and the varistor function was lost Problem.

Experimental Example 2. Varistor Observation of microstructure of ceramics

The microstructure of the varistor ceramics prepared in Examples 1 to 2 and Comparative Examples 1 to 6 was observed with a scanning electron microscope. The results are shown in Figs. 2 to 5. FIG. 2 is an image of a surface of a varistor ceramic manufactured by sintering at 1200 ° C, and FIG. 3 is an image of a fracture surface of a varistor ceramic manufactured by sintering at 1200 ° C. FIG. 4 is an image of a surface of a varistor ceramic manufactured by sintering at 1350 ° C., and FIG. 5 is an image of a fracture surface of a varistor ceramic manufactured by sintering at 1350 ° C. FIG.

2 to 5, it was confirmed that as the content of barium titanate increases, the size of the fine particles decreases, and it can be seen that the microstructure is affected by the content of barium titanate contained in the varistor ceramics .

Claims

Praseodymium-based zinc oxide and barium titanate (BaTiO ₃ )
The atomic percentage ratio of barium titanate to praseodymia based zinc oxide is 88 to 99: 1 to 12,
The praseodymium-based zinc oxide comprises 90 to 92% by weight of ZnO, 0.3 to 0.5% by weight of Pr ₆ O ₁₁ , 2 to 3% by weight of Co ₃ O ₄ based on the total weight of the praseodymia- 0.3 to 0.5% by weight of Nd ₂ O ₃ ,
Characterized in that the breakdown voltage is from 100 to 800 V at 1 mA, the electrostatic capacity at 1 kHz is from 50 to 400 pF, and the relative dielectric constant is from 500 to 3000 when measured by a curve tracer.

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The method according to claim 1,
Wherein the varistor ceramics are sintered at 1300 to 1400 ° C.

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The method according to claim 1,
Wherein the varistor ceramics have a capacitance of 50 to 300 pF at 1 MHz and a relative dielectric constant of 500 to 2,500.

A thin film comprising the varistor ceramic of any one of claims 1, 3 and 6.

The thin film according to claim 7, wherein the thin film is hetero-bonded to the capacitor layer.

A mixture of praseodymia based zinc oxide and barium titanate (BaTiO ₃ ) in an atomic ratio of 88 to 99: 1 to 12 to prepare a mixture;
Crushing and filtering the mixture and drying it;
3) pulverizing and filtering the dried mixture to obtain powder;
Adding powdered PVB (polyvinyl butyral) powder to the pulverized mixture and granulating it; And
And sintering the granulated mixture at a temperature of 1300 to 1400 DEG C,
The praseodymium-based zinc oxide comprises 90 to 92% by weight of ZnO, 0.3 to 0.5% by weight of Pr ₆ O ₁₁ , 2 to 3% by weight of Co ₃ O ₄ based on the total weight of the praseodymia- 0.3 to 0.5% by weight of Nd ₂ O ₃ ,
The manufactured varistor ceramics had a breakdown voltage of 100 to 800 V at 1 mA, a capacitance of 50 to 400 pF at 1 kHz, and a relative dielectric constant of 500 to 3000 when measured with a curve tracer .

10. The method of claim 9,
Wherein the drying in step 2 is performed at 70 ° C to 90 ° C for 1 to 3 hours.

10. The method of claim 9,
Wherein the PVB (polyvinyl butyral) powder is mixed in an amount of 5 to 10 wt% with respect to the powder mixture in the step 3.

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