WO2016178536A2 - Varistor ceramic and method for producing same - Google Patents

Abstract

Provided is varistor ceramic. The varistor ceramic according to one embodiment of the present invention comprises praseodymia-based zinc oxide and strontium titanate (SrTiO₃), wherein the atomic percent of strontium titanate ratio with respect to praseodymia-based zinc oxide is 92-99:8-1. Accordingly, the present invention improves ESD tolerance, has superb electrostatic capacity, and can exhibit stability in a heterojunction.

Description

Varistor ceramic and its manufacturing method

The present invention relates to a varistor ceramic and a manufacturing method thereof, and more particularly, to a varistor ceramic and a method for manufacturing the same, which can improve ESD resistance, have excellent capacitance, and exhibit stability in heterojunction.

Modern information technology (IT) industry is progressing day by day with the development of semiconductor industry. Electric, electronic, and information communication devices are made thin and small in appearance and functionally complex by using highly integrated electronic information and communication devices. It is being advanced in the direction of multifunctionality.

On the other hand, high integration of electronic information communication devices causes a possibility to react more sensitively in a transient situation, which can be a fatal weakness in securing the reliability of the entire system. The causes of such transients include lightning, lightning, nuclear electromagnetic waves, high-energy switching, or electrostatic discharge (ESD), among which electrostatic discharge (ESD) and induction are the first considerations for protecting electronic circuits. There are two types of inductive loads. For this reason, in line with the high integration of electronic information communication devices, various methods for protecting electronic circuits from transient situations have been devised. The best method in terms of performance and economics is the use of surge protection devices.

Among these, zinc oxide varistors (ZnO varistors) are surge protection devices that protect the protected devices by releasing abnormal voltages, currents, and energies, ie, surges, drawn from the front end of the protected devices including electronic devices to ground. Or modularized and widely used throughout the industry. Zinc oxide varistors, which are polycrystalline ceramics, are characterized by having a sorption-absorbing ability by showing that the grain boundaries of the zinc oxide grain pairs are selectively converted into insulating or conductive depending on the applied voltage, thereby exhibiting nonlinear electrical behavior. .

In other words, zinc oxide varistors are non-linear resistors whose resistance varies with voltage, and are connected in parallel to the protector, and normally operate as an insulator that exhibits high impedance. The discharge of high energy protects the protected group.

Zinc oxide varistors prepared by adding a small amount of non-linear inducing oxides and oxides for improving properties to zinc oxide, which occupy most of ceramics, are classified into various types according to the types of non-linear inducing oxides. ), Followed by praseodymium (Pr). ZnO-based varistors formed of ZnO-Bi-based or ZnO-Pr-based materials in the varistor material composition system have better voltage nonlinearity and better surge current resistance than SiC-based varistors and SrTiO3-based varistors. It is used as a material of surge protection device because of its ability to protect electronic devices.

However, the ZnO-Bi varistor is composed of Bi ₂ O ₃ , Sb ₂ O ₃ , Mn, Co, Ni, Cr, glass frit, Al, K, etc. The Bi ₂ O component is ESD (Electro-Static) Since the discharge resistance is weak, ZnO-Bi-based varistors including the same have disadvantages of poor ESD characteristics. In addition, since the Sb ₂ O ₃ component is classified as a carcinogen and the concentration is regulated, the ZnO-Bi-based varistor including the same has a disadvantage in that it is not free to manufacture. In addition, ZnO-Pr-based varistors have a good voltage non-linearity, but have a disadvantage in that leakage current is greater than that of ZnO-Bi-based varistors. There is a disadvantage in that the manufacturing cost is high because it requires a large amount of expensive components (Pd and the like).

On the other hand, in recent years, high-density mounting is rapidly progressing due to the miniaturization and miniaturization of surface-mount devices (SMDs) and miniaturization of electronic components according to the trend of lighter and shorter and higher functionalization of electronic devices. Since the signal rates of circuits in SMD electronics range from several hundred MHz to several GHz, it is necessary to significantly lower the capacitance of the varistor to prevent signal delays at such high signal rates.

Since ZnO-type varistors have high dielectric constants of up to several hundreds, in order to have a small capacitance, the electrode area must be considerably reduced. However, reducing the electrode area to have a small capacitance results in a reduction in surge resistance, which also leads to a problem that the varistor manufacturing process is quite difficult. Therefore, there is a need for a ZnO type varistor having a low dielectric constant.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and provides an varistor ceramic and a method for manufacturing the same, which exhibit improved ESD resistance, excellent capacitance, and stability in heterojunction.

In order to solve the above problems, the present invention comprises praseodymia-based zinc oxide and titanium strontium oxide (SrTiO ₃ ), the atomic percentage ratio of praseodymia-based zinc oxide and titanium strontium oxide is 92 ~ 99: 8 It provides a varistor ceramic, characterized in that ~ 1.

In one embodiment of the present invention, the praseodymia-based zinc oxide comprises ZnO, Pr ₆ O ₁₁ , Co ₃ O ₄ and Nd ₂ O ₃ , the total weight of the praseodymia-based zinc oxide ZnO 90 ~ 95 wt%, Pr ₆ O ₁₁ 0.5 to 1% by weight, Co ₃ O ₄ 2 to 5% by weight and Nd ₂ O ₃ 0.5 to 1% by weight.

In addition, the varistor ceramic may be sintered at 1300 ~ 1400 ℃.

In addition, the varistor ceramic may have a breakdown voltage of 100 to 900 V at 1 mA when measured by a curve tracer.

In addition, the varistor ceramic may have a capacitance of 1 to 10 pF and a dielectric constant of 100 to 500 at 1 kW.

In addition, the varistor ceramic may have a capacitance of 1 to 50 pF and a dielectric constant of 200 to 500 at 1 MHz.

The present invention also provides a thin film comprising the varistor ceramic according to the present invention.

In one embodiment of the present invention, the thin film may be heterojunction with the capacitor layer.

In addition, the present invention is a step of preparing a mixture by mixing the praseodymia-based zinc oxide and titanium strontium oxide (SrTiO ₃ ) in an atomic ratio of 92 ~ 99: 8 ~ 1; Grinding and filtering the mixture and drying the mixture; Pulverizing and filtering the dried mixture to three steps; Adding granulated polyvinyl butyral (PVB) powder to the powdered mixture, followed by granulation; And a step 5 of sintering the granulated mixture under pressure molding.

In one embodiment of the present invention, the drying in the second step may be performed for 1 to 3 hours at 70 ℃ ~ 90 ℃.

In addition, the polyvinyl butyral (PVB) powder may be mixed in an amount of 5 wt% to 10 wt% with respect to the mixture powdered in step 3.

In addition, the five steps of sintering may be performed at 1300 ~ 1400 ℃.

The varistor ceramic according to the present invention is very excellent in ESD resistance, excellent in capacitance, and may exhibit stability in heterojunction. In addition, according to the trend of light and short size miniaturization of electronic devices can be widely applied to a variety of electronic devices, such as to have a resistance to the surge voltage of the high voltage introduced into the chip.

1 is an image showing a mold of the varistor ceramic according to the present invention.

2 is an image observing the surface of the varistor ceramic prepared by sintering at 1200 ℃.

Figure 3 is an image of the fracture surface of the varistor ceramic prepared by sintering at 1200 ℃.

4 is an image observing the surface of the varistor ceramic prepared by sintering at 1350 ℃.

5 is an image of the fracture surface of the varistor ceramic produced by sintering at 1350 ℃.

6 is a graph showing breakdown voltages of Comparative Examples 3 to 6. FIG.

7 is a graph showing breakdown voltages of Examples 1 and 2 and Comparative Examples 1 and 2. FIG.

8 is a graph showing the dielectric constant of Examples 1-2 and Comparative Examples 1-2.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification.

The present invention includes praseodymium-based zinc oxide and titanium strontium oxide (SrTiO ₃ ), and the atomic percentage ratio of praseodymium-based zinc oxide and titanium strontium oxide is 92 to 99: 8 to 1, varistor characterized in that Provide ceramic. Hereinafter, the present invention will be described in more detail.

The varistor ceramic according to the present invention has an effect of improving the electrostatic discharge (ESD) resistance, excellent capacitance, and stability in heterojunction by mixing in the above ratio.

At this time, the atomic percentage ratio of the praseodymia-based zinc oxide and titanium strontium oxide is preferably 92 to 99: 8 to 1, more preferably 96 to 98: 4 to 2. When the atomic percentage ratio of the praseodymia-based zinc oxide and titanium strontium oxide exceeds 99: 1, the dielectric constant of the manufactured varistor ceramic is high, but the capacitance is lowered, so that the function as a varistor is lost. In this case, there is a problem due to high break down voltage.

In this case, 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 , ZnO 90 ~ 95% by weight, Pr ₆ O ₁₁ based on the total weight of the praseodymia zinc oxide 0.5 to 1% by weight, Co ₃ O ₄ 2 to 5% by weight and Nd ₂ O ₃ 0.5 to 1% by weight. If the content ratio is not satisfied as described above, it may not be easy to achieve the desired physical properties of the present invention.

In the varistor ceramic according to the present invention, the varistor ceramic may be sintered at 1300 ~ 1400 ℃. When the varistor ceramic is sintered at a temperature of less than 1300 ℃ there is a problem that can lose the varistor characteristics, if the sintered at a temperature exceeding 1400 ℃ there is a problem that the function of the varistor is deteriorated and leakage current may increase .

In the varistor ceramic according to the present invention, the varistor ceramic may have a breakdown voltage of 100 to 900 V at 1 mA, and a breakdown voltage of 500 to 900 V at 1 mA, as measured by a curve tracer. Can be represented.

In addition, the varistor ceramic may have a capacitance of 1 to 10 pF, a dielectric constant of 100 to 500, a capacitance of 1 to 50 pF, and a dielectric constant of 200 to 500 at 1 MHz.

Varistor ceramics according to the present invention can exhibit the physical properties as described above can be manufactured to exhibit a wide range of voltage and capacitance. In addition, by applying a relatively simple addition method can exhibit the effect of artificially controlling a variety of electrical properties based on the same composition.

The present invention also provides a thin film comprising the varistor ceramic described above. The thin film may be heterojunction with the capacitor layer to be disposed at an appropriate position according to the desired characteristics, thereby controlling the dielectric constant and voltage to implement the desired characteristics.

In addition, the present invention is a step 1 of preparing a mixture by mixing the praseodymia-based zinc oxide and titanium strontium oxide (SrTiO ₃ ) in an atomic ratio of 92 to 99: 1 to 8; Grinding and filtering the mixture and drying the mixture; Pulverizing and filtering the dried mixture to three steps; Adding granulated polyvinyl butyral (PVB) powder to the powdered mixture, followed by granulation; And a step 5 of sintering the granulated mixture under pressure molding. Hereinafter, the present invention will be described in more detail step by step.

In the method of manufacturing a varistor ceramic according to the present invention, the first step is to prepare a mixture by mixing the praseodymia-based zinc oxide and titanium strontium oxide (SrTiO ₃ ) in an atomic ratio of 92 ~ 99: 8 ~ 1 In the above mixture, the atomic percentage ratio of praseodymia zinc oxide and titanium strontium oxide is preferably 92 to 99: 8 to 1, more preferably 96 to 98: 4 to 2. When the atomic percentage ratio of titanium strontium oxide to praseodymia-based zinc oxide exceeds 99: 1, the dielectric constant of the produced varistor ceramic is high, but the capacitance decreases, so that the function as a varistor is lost. If less, there is a problem due to high break down voltage.

In addition, 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 , ZnO 90 ~ 95% by weight, Pr ₆ O ₁₁ based on the total weight of the praseodymia zinc oxide 0.5 to 1% by weight, Co ₃ O ₄ 2 to 5% by weight and Nd ₂ O ₃ It may include 0.5 to 1% by weight, through which the present invention can more easily express the desired physical properties.

In the method of manufacturing a varistor ceramic according to the present invention, the second step is a step of pulverizing, filtering and drying the mixture, which may be pulverized by milling the mixture in order to powder the mixture. At this time, the drying in the second step is preferably carried out for 1 to 3 hours at 70 ℃ ~ 90 ℃, more preferably it is carried out for 2 to 3 hours at 80 ℃ ~ 90 ℃.

In the method of manufacturing a varistor ceramic according to the present invention, the three step is to pulverize the powder mixture by pulverization and filtration, the pulverization may be carried out through a mortar and filtration through a standard mesh Can be.

In the method of manufacturing a varistor ceramic according to the present invention, the step 4 is a step of granulating after adding a polyvinyl butyral (PVB) powder to the powdered mixture, wherein the PVB for the mixture powdered in the step 4 (Polyvinyl butyral) powder can be mixed in 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 adhesiveness between the raw materials when uniaxial pressure molding is introduced when less than 5% by weight does not maintain the shape of the corner portion after uniaxial pressure molding cracking or crushing This, when introduced in excess of 10% by weight is difficult to drop off the molding mold due to excessive adhesive strength and there is a problem in that the sinterability is poor due to excessive volume increase.

In the method for manufacturing a varistor ceramic according to the present invention, the step 5 is a step of sintering the granulated mixture after pressing, the electrical properties of the varistor ceramic according to the present invention can be controlled through the sintering temperature. . The sintering of the five steps may be carried out at 1300 ~ 1400 ℃, preferably 1340 ~ 1400 ℃ can be easier to implement a varistor ceramic expressing the desired physical properties of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the following examples. The following examples are presented 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) ZnO (90 to 95% by weight), Pr ₆ O ₁₁ (0.5 to 1% by weight), Co ₃ O ₄ (2 to 5% by weight), Nd ₂ O ₃ (0.5 to 1% by weight) mixed Then, prepared by calcining at 800 ° C. for 2 hours, Praseodymia-based zinc oxide and perovskite oxide titanium strontium oxide (SrTiO ₃ ) were mixed in a 250 ml plastic bottle at an atomic ratio of 97: 3.

(2) After introducing ZrO ₂ balls into the mixture, milling was performed for 24 hours at a speed of 250 rpm in a milling machine (milling M / C). The mixture was prepared through the ball mill pulverization, and the mixture was recovered, filtered through a 200 mesh sieve, and dried for 2 hours at 80 ° C. using an electric oven for the filtered slurry.

(3) The dried powder was ground using a mortar and pestle, and then filtered using a standard mesh (ASTM mesh No. 500 = 25 μm).

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

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

Example 2 Preparation of Varistor Ceramics

A varistor ceramic was manufactured in the same manner as in Example 1, except that the praseodymia-based zinc oxide and titanium strontium oxide were mixed at an atomic ratio of 95: 5.

Comparative Example 1. Fabrication of Varistor Ceramic

A varistor ceramic was manufactured in the same manner as in Example 1, except that only praseodymia-based zinc oxide was used.

Comparative Example 2. Fabrication of Varistor Ceramic

A varistor ceramic was manufactured in the same manner as in Example 1, except that the praseodymia-based zinc oxide and titanium strontium oxide were mixed at an atomic ratio of 90:10.

Comparative Example 3. Fabrication of Varistor Ceramic

A varistor ceramic was manufactured in the same manner as in Example 1, except that only praseodymia-based zinc oxide was used and sintered at 1200 ° C.

Comparative Example 4. Fabrication of Varistor Ceramic

A varistor ceramic was prepared in the same manner as in Example 1, except that the praseodymia-based zinc oxide and titanium strontium oxide were mixed at an atomic ratio of 97: 3 and sintered at 1200 ° C.

Comparative Example 5. Fabrication of Varistor Ceramic

A varistor ceramic was manufactured in the same manner as in Example 1, except that the praseodymia-based zinc oxide and titanium strontium oxide were mixed at an atomic ratio of 95: 5, and sintered at 1200 ° C.

Comparative Example 6. Preparation of Varistor Ceramic

A varistor ceramic was manufactured in the same manner as in Example 1, except that the praseodymia-based zinc oxide and titanium strontium oxide were mixed at an atomic ratio of 90:10 and sintered at 1200 ° C.

Experimental Example

Experimental Example 1. Analysis of electrical characteristics of varistor ceramic

After measuring the thickness and diameter of the varistor ceramic prepared in Examples 1 to 2 and Comparative Examples 1 to 6, the density was measured. In addition, after the electrode printing was performed on the front and back of the varistor ceramic, the electrode baking was performed, and when the electrode baking was completed, it was recovered and the breakdown voltage, the leakage current, and the dielectric characteristics were obtained using a programmable curve tracer (Tektronix 370B). Was measured. The results are shown in Table 1 below. In addition, the breakdown voltages of Examples 1 to 2 and Comparative Examples 1 to 6 are shown in FIGS. 6 and 7, and dielectric constants are shown in FIG. 8.

At this time, the breakdown voltage indicated as unmeasured exceeded 2000 V which is the measurement limit voltage of the curve tracer.

	Pr-Zn: SrTiO3	Density (g / cm3)	Vn	V / mm	IL	Cp (pF @ 1㎑)	Permittivity (1㎑)	Cp (pF @ 1MHz)	Dielectric constant (1MHz)
Example 1	97: 3	5.34	555.8	512.81	7.77	39.56	327.64	29.66	245.65
Example 2	97: 5	5.47	808.4	782.77	0.52	53.68	408.08	40.78	309.66
Comparative Example 1	100: 0	5.27	59	52	38.04	1195.9	9269.75	476	3713.38
Comparative Example 2	90: 10	5.34	Not measurable	-	-	8.72	69.4	7.86	62.56
Comparative Example 3	100: 0	5.24	1093	1066	0.12	23.54	164.09	13.34	93
Comparative Example 4	97: 3	5.4	Not measurable	-	-	3.57	23.88	2.48	16.6
Comparative Example 5	95: 5	5.39	Not measurable	-	-	3.59	26.31	2.56	18.73
Comparative Example 6	90: 10	5.23	Not measurable	-	-	5.14	36.14	4.08	28.69

According to Table 1, in Examples 1 to 2, the breakdown voltage is 100 to 900 V and the atomic percentage ratio of titanium strontium oxide to the praseodymia zinc oxide is 92 to 99: 1 to 8. It was confirmed that the capacitance at 1 mA is 10 to 60 pF, and the dielectric constant is 100 to 500. In addition, at 1 MHz, it was confirmed that the capacitance was 10 to 50 pF, and the dielectric constant was 200 to 500 (unit). However, in the case of Comparative Examples 1 to 2 outside the above range, the dielectric constant decreased or increased significantly at 1 ㎑ and 1 MHz, and the breakdown voltage showed a significantly lower value of 100 V or less, or was impossible to measure beyond 2000 V, so that the function of the varistor It showed a problem of losing.

In addition, Comparative Examples 3 to 6 are varistor ceramics manufactured by sintering at 1200 ° C., but there is a problem that varistor characteristics disappear, but the breakdown voltage is remarkably high, and thus it can be used as an insulator.

Experimental Example 2 Observation of Microstructure of Varistor Ceramic

The microstructures of the varistor ceramics prepared in Examples 1 to 2 and Comparative Examples 1 to 6 were observed by a scanning electron microscope, and the results are shown in FIGS. 2 to 5. At this time, Figure 2 is an image of the surface of the varistor ceramic prepared by sintering at 1200 ℃, Figure 3 is an image of the fracture surface of the varistor ceramic prepared by sintering at 1200 ℃. 4 is an image observing the surface of the varistor ceramic produced by sintering at 1350 ℃, Figure 5 is an image of the fracture surface of the varistor ceramic produced by sintering at 1350 ℃.

2 to 5, it was confirmed that the size of the microparticles decreases as the content of titanium strontium oxide increases, and through this, the microstructure is affected by the content of the titanium strontium oxide contained in the varistor ceramic. Could.

Claims (12)

1. Praseodymia-based zinc oxide and titanium strontium oxide (SrTiO ₃ ),

   A varistor ceramic having an atomic percentage ratio of praseodymia zinc oxide and titanium strontium oxide of 92 to 99: 8 to 1.
2. The method of claim 1,

   The praseodymia zinc oxide comprises ZnO, Pr ₆ O ₁₁ , Co ₃ O ₄ and Nd ₂ O ₃ ,

   ZnO 90 to 95% by weight, Pr ₆ O ₁₁ 0.5 to 1% by weight, Co ₃ O ₄ 2 to 5% by weight and Nd ₂ O ₃ 0.5 to 1% by weight based on the total weight of the praseodymia zinc oxide Varistor ceramic comprising a.
3. The method of claim 1,

   The varistor ceramic is a varistor ceramic sintered at 1300 ~ 1400 ℃.
4. The method of claim 1,

   The varistor ceramic is a varistor ceramic having a breakdown voltage of 100 ~ 900 V at 1 mA, measured by a curve tracer.
5. The method of claim 1,

   The varistor ceramic is a varistor ceramic having a capacitance of 1 ~ 10 ~ 60 pF, the dielectric constant of 100 ~ 500.
6. The method of claim 1,

   The varistor ceramic has a capacitance of 1 to 50 pF and a dielectric constant of 200 to 500 varistor ceramic at 1 MHz.
7. Thin film comprising a varistor ceramic according to claim 1.
8. The thin film of claim 7, wherein the thin film is heterojunction with a capacitor layer.
9. Praseodymia-based zinc oxide and titanium strontium oxide (SrTiO ₃ ) 1 to 92 by mixing in an atomic ratio of 99: 8 to 1 step to prepare a mixture;

   Grinding and filtering the mixture and drying the mixture;

   Pulverizing and filtering the dried mixture to three steps;

   Adding granulated polyvinyl butyral (PVB) powder to the powdered mixture, followed by granulation; And

   Method for producing a varistor ceramic comprising a; 5 step of sintering the granulated mixture by pressing.
10. The method of claim 9,

    Drying in the second step is a method for producing a varistor ceramic for 1 to 3 hours at 70 ℃ ~ 90 ℃.
11. The method of claim 9,

    Method for producing a varistor ceramic for mixing the polyvinyl butyral (PVB) powder in 5 to 10% by weight with respect to the mixture powdered in step 3.
12. The method of claim 9,

    The sintering of the five steps is a method for producing a varistor ceramic to be carried out at 1300 ~ 1400 ℃.

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