KR20130127801A - Vanadium-based zinc oxide varistor and manufacturing method for the same - Google Patents

Abstract

The present invention relates to a zinc oxide varistor, especially a vanadium-based zinc oxide (ZnO-V2O5-) chip varistor composition which can be plasticized with a silver internal electrode at the same time. The present invention relates to the vanadium-based zinc oxide varistor and a manufacturing method thereof which is capable of securing the excellent nonlinearity of the varistor and stably maintaining the nonlinearity of the varistor after using for a long time by adding small amount of erbium into the vanadium-based zinc oxide varistor and adjusting the content of the erbium to be less than 0.1 mol%.

Description

Technical Field The present invention relates to a vanadium-based zinc oxide varistor and a manufacturing method thereof,

The present invention relates to a zinc oxide varistor and particularly to a vanadium-based zinc oxide (ZnO-V ₂ O ₅ -) chip varistor composition capable of co-firing with a silver (Ag) internal electrode. The vanadium oxide zinc varistor contains a small amount of erbium The present invention relates to a vanadium-based zinc oxide varistor capable of securing excellent nonlinearity of a varistor by controlling the content thereof and maintaining nonlinearity of the varistor more stably even when used for a long time, and a method for producing the varistor.

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.

However, a bismuth-based and praseodymium-based zinc oxide varistor has a disadvantage in that it can not be co-fired with a silver (Ag) internal electrode when constituted by a multilayer chip element. This is because at a temperature of 1000 or more, Because of the process limitations that must be sintered.

In order to solve these limitations, researches on ZnO-V ₂ O ₅ (vanadium) varistors have been actively conducted. The advantage of the ZnO-V ₂ O ₅ varistor is that it can be sintered at a relatively low temperature near 900, which is below the melting point of silver, so that expensive metals such as palladium (Pd) or platinum (Pt) It is possible to perform co-firing by using silver (Ag) which is less expensive.

However, studies on vanadium-based varistors have remained in the early stage and it is reported that appropriate additives are required to obtain high nonlinearity, and only MnO ₂ and Nb ₂ O ₅ are introduced as additives.

In addition, the surge absorption capacity of zinc oxide varistor is improved as the absolute value of the nonlinear coefficient is higher. However, the nonlinear coefficient of the vanadium varistor is still close to 30, so it is not enough to be put to practical use.

Accordingly, research and development of a new vanadium-based varistor material and its composition, which can ensure high nonlinearity of the vanadium-based varistor and maintain the non-linearity of the varistor more stably even when used for a long time, is demanded more desperately.

The object of the present invention is to find a novel additive contained in a vanadium-based zinc oxide varistor in a trace amount, thereby realizing high nonlinearity which is essentially required for a varistor which is a nonlinear resistor element.

Another object of the present invention is to provide a vanadium-based zinc oxide varistor which is practically useful by determining the appropriate content of a new additive capable of securing stability of non-linearity even when the vanadium-based zinc oxide varistor is used for a long time, and a method for producing the same. .

The present invention relates to a vanadium oxide zinc varistor comprising zinc oxide (ZnO) as a main component and vanadium oxide (V ₂ O ₅ ), manganese oxide (MnO ₂ ) and niobium oxide (Nb ₂ O ₅ ) Wherein erbium oxide (Er ₂ O ₃ ) is further added to the vanadium-based zinc oxide varistor.

Here, the erbium oxide (Er ₂ O ₃ ) is preferably added in an amount of 0.1 mol% or less.

It is further preferable that the erbium oxide (Er ₂ O ₃ ) is added in an amount of 0.05 mol%.

The vanadium-based zinc oxide varistor has a breakdown field (E _1mA ) of 5,000 V / cm or more and a nonlinear coefficient (a) of 50 or more.

The vanadium-based zinc oxide varistor may have a composition of (97.4-X) mol% ZnO + 0.5 mol% V ₂ O ₅ + 2.0 mol% MnO ₂ + 0.1 mol% Nb ₂ O ₅ + X mol% Er ₂ O ₃ .

The method of manufacturing a vanadium-based zinc oxide varistor according to the present invention comprises the steps of preparing zinc oxide (ZnO), vanadium oxide (V ₂ O ₅ ), manganese oxide (MnO ₂ ), niobium oxide (Nb ₂ O ₅ ) and erbium oxide a first step of weighing the ₂ O _3); and, the second step of the weighed composition mixed by ball milling by addition of acetone; and the mixture subjected to the second step of the polyvinyl butyral (PVB) binder and A third step of mixing and kneading the mixture into a container containing acetone and drying the mixture; and a fourth step of making the mixed composition into a desired shape and sintering and then polishing both surfaces of the sintered body; And a fifth step of applying a silver electrode to the polished sintered body and performing a package treatment.

Here, the erbium oxide (Er ₂ O ₃ ) is preferably added in an amount of 0.1 mol% or less.

It is further preferable that the erbium oxide (Er ₂ O ₃ ) is added in an amount of 0.05 mol%.

The composition of the vanadium-based zinc oxide varistor according to the above production method is (97.4-X) mol% ZnO + 0.5 mol% V ₂ O ₅ + 2.0 mol% MnO ₂ + 0.1 mol% Nb ₂ O ₅ + X mol% Er ₂ O ₃ .

The present invention has an excellent effect of securing a very high level of nonlinearity which is difficult to realize in a conventional zinc oxide varistor by applying erbium as an additive contained in a vanadium-based zinc oxide varistor in a trace amount.

Also, the vanadium-based zinc oxide varistor of the present invention has an advantage in that it can secure excellent fineness such that the nonlinearity is not largely deteriorated even after long-time use, by controlling the content of erbium as an additive.

FIG. 1 is a transcriptional scanning micrograph of four specimens of a vanadium-based zinc oxide varistor with different contents of erbium.
FIG. 2 is a view showing an XRD pattern of each specimen shown in FIG. 1; FIG.
3 is a graph showing voltage-current characteristics according to an erbium content of a vanadium-based zinc oxide varistor specimen according to the present invention.
4 is a graph showing changes in voltage-current (EJ) characteristics versus erbium content.
Fig. 5 is a graph showing changes in leakage current over time of the DC accelerated aging stress test of the vanadium-based zinc oxide varistor specimen of Fig. 3; Fig.
6 is a graph comparing the voltage-current characteristics of the vanadium-based zinc oxide varistor specimen of FIG. 5 before and after the DC accelerated aging stress test.

Hereinafter, the most preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the process for preparing the vanadium-based zinc oxide varistor according to the present invention and the process for evaluating the structural and electrical characteristics of the vanadium-based zinc oxide varistor will be described in detail.

Production of specimen

The composition of the vanadium-based zinc oxide varistor according to the present invention is composed of ZnO, V ₂ O ₅ , MnO ₂ , Nb ₂ O ₅ and Er ₂ O _3. V ₂ O ₅ , MnO ₂ , Nb ₂ O ₅ The composition of the specimen was fixed and the content of erbium oxide Er ₂ O ₃ added as a main component ZnO and a small amount was changed.

The content of Er ₂ O ₃ was 0.0, 0.05, 0.1, 0.25 mol%, and the contents of V ₂ O ₅ , MnO ₂ and Nb ₂ O ₅ were fixed to 0.5 mol%, 2.0 mol% and 0.1 mol% To prepare four kinds of specimens.

Therefore, the composition used in the preparation of the specimen is (97.4-X) mol% ZnO + 0.5 mol% V ₂ O ₅ + 2.0 mol% MnO ₂ + 0.1 mol% Nb ₂ O ₅ + X mol% Er ₂ O ₃ 0.0, 0.05, 0.1, 0.25).

Each sample of high purity was weighed to an error range of 10 with an electronic balance, and zirconia balls, acetone and each weighed sample were placed in a polypropylene container and mixed by ball milling for 24 hours.

The mixture slurry was again mixed in a container containing 0.8% (weight percentage) of polyvinylbutylalcohol (PVB) binder and acetone, which was dried and then sieved into a 100 mesh sieve.

The powder prepared in the above process was molded into disk-shaped pellets so that the diameter was 10 mm and the thickness was 1.5 mm under uniaxial pressure of 100 MPa, and sintered at 900 sintering temperature in air for 3 hours. After sintering, Lt; / RTI > Sintering and cooling proceeded at a rate of 4 and a minute respectively.

The final specimen was lapped / polished to a diameter of 8 mm and a thickness of 1.0 mm. Both surfaces of the processed specimens were coated with a silver paste, and a silver electrode with a diameter of 5 mm was heat-treated at 550 for 10 minutes .

Finally, lead wires were soldered to the silver electrodes on each side, and dipped into a thermoplastic resin powder to make a package.

Microstructure characteristics

The surface of the specimen prepared above was wrapped with SiC abrasive paper, mirror-polished with 0.3 Al ₂ O ₃ powder, and then chemically etched in a ₁ HClO ₄ : 1000 H ₂ O solution for 25 to 25 seconds. And observed with an electron microscope (FESEM, Quanta 200, FEI, Brno, Czech).

The average grain size, d, is calculated by the linear crossing equation d = 1.56L / MN, where L is any test line on the microscope photograph, M is the magnification of the microscope image, N is the effective Crossing number).

The crystalline phase was identified by XRD (X-ray diffractometer, X'pert-Pro MPD, Panalytical, Almelo, Netherland) using CuK _a radiation filtered with nickel.

The sintered density () was measured using a density measuring kit (238490) attached to an electronic balance (AG 245, Mettler Toledo International Inc., Greifensee, Switzerland).

FIG. 1 is a transcriptional scanning micrograph of four specimens of a vanadium-based zinc oxide varistor with different contents of erbium, and four specimens for 0.0, 0.05, 0.1 and 0.25 mol% of erbium (Er ₂ O ₃ ) (A), (b), (c), and (d), respectively.

As shown in Fig. 1, it can be seen that the surface morphology in which the particles are uniformly distributed and the grain boundary is clear in all the specimens is confirmed.

The average grain size (d) decreased from 5.5 to 5.2 up to 0.05 mol% of erbium content, but increased to 5.7 as the erbium content increased to 0.25 mol%.

Sintered density () is proportional to the increase in the erbium content were increased from 5.51g / cm ³ to 5.61g / cm ^3, which respectively correspond to 95.1% and 96.4% of the theoretical density (5.78g / cm ³⁾ of zinc oxide will be. Therefore, the addition of erbium can be evaluated as having a positive effect of enhancing the grain growth of the vanadium-based zinc oxide varistor.

FIG. 2 shows XRD patterns for the four specimens in which Zn ₃ (VO ₄ ) ₂ , ZnV ₂ O ₄ , V ₂ O ₅ and Mn-rich phases were added in addition to the main crystal phase of hexagonal zinc oxide And is present as a sub-crystalline phase. Particularly, erbium-containing specimens (b) to (d) show that ErVO ₄ is present as a crystalline phase in comparison with erbium-free specimen (a).

Electrical characteristic measurement

The electrical properties of the specimens were evaluated using voltage-current (E-J) characteristics, measured using a High Voltage Source-Measure Unit (Keithley 237, Keithley Instruments Inc., Cleveland, OH, USA).

Here, the breakdown field (E _{1 mA} ) was defined as the voltage at a current density of 1.0 mA / cm ² and the leakage current density (J _A ) at a current of 0.80 E _{1 mA} .

The nonlinear coefficient (a) was calculated by the following equation (1).

_{a = (logJ 2 -logJ 1)} / (logE 2 -logE 1) ....................... (1)

(Where J ₁ = 1.0 mA / cm ² , J ₂ = 10 mA / cm ² , E ₁ and E ₂ are voltages corresponding to J ₁ and J ₂ , respectively)

FIG. 3 shows voltage-current (E-J) characteristics for four specimens varying the content of erbium, and the characteristics of the varistor make the voltage-current (E-J) curve nonlinear.

The voltage-current (E-J) characteristic curve is divided into two distinct regions. One is an ohmic region of extremely high impedance before the breakdown field and the other is a non-ohmic region of extremely low impedance after the breakdown field. The current density rapidly rises to the boundary of the breakdown field. Therefore, it is shown that the characteristics of the varistor are superior as the slope change (knee) of the voltage-current (E-J) characteristic curve between the two regions increases.

3, when a 0.05 mol% and 0.1 mol% erbium (Er ₂ O ₃ ) is added, the slope of the voltage-current (EJ) characteristic curve becomes more pronounced, .

The detailed voltage-current (E-J) characteristics for each specimen are summarized in Table 1 below.

Microstructure and voltage-current (E-J) characteristic parameters for the four specimens of the present invention Psalter d
(탆) ρ *
(g / cm ³⁾ E _1mA
(V / cm) v _gb
(V / gb) alpha J _L
(/ / Cm ² ) (a) 5.5 5.51 4800 2.6 44.9 95 (b) 5.2 5.53 5444 2.8 63.4 73 (c) 5.3 5.54 5266 2.8 51.1 100 (d) 5.7 5.61 5061 2.3 14.8 399

* Theoretical density of zinc oxide (ZnO): 5.78 g / cm ³

5 is a graph showing the characteristics of a breakdown field (E _1mA ), a nonlinear coefficient (a), and a leakage current density (J _A ) according to changes in the content of erbium.

Referring to FIG. 5A showing the results of Table 1, the breakdown field is increased from 4800 V / cm to 5444 V / cm as the erbium (Er ₂ O ₃ ) content reaches 0.05 mol% As the content of erbium increased further, it decreased to 5061 V / cm at an erbium concentration of 0.25 mol%.

The behavior of the breakdown field (E _1mA ) according to the content of erbium as described above can be explained by the average grain size (d) of zinc oxide.

The relationship between breakdown electric field and the mean grain size of E _1mA = v _gb / d is represented from the equation of (wherein, d is the size of the crystal grains, v _gb is input gyedang breakdown voltage), the above formula (E _1mA = v _gb / As can be seen in d), the breakdown field (E _1mA ) is directly determined by the average grain size (d) and the breakdown voltage per grain (v _gb ). Referring to Table 1, the breakdown voltage per grain according to the concentration of erbium shows almost the same level. In this state, the increase in the average grain size (d) leads to a decrease in the number of grain boundaries, The electric field is reduced.

The nonlinear coefficient (a) is shown in FIG. 5 (b). The nonlinear coefficient (a) is 63.4 when the erbium (Er ₂ O ₃ ) content is 0.05 mol% And decreased with increasing erbium content and decreased to 14.8 at 0.25 mol% erbium concentration. As can be seen from FIG. 5, the behavior of the breakdown field (E _1mA ) and the nonlinear coefficient (a) according to the content of erbium shows a similar pattern, and in any case, the content of erbium has a significant influence.

The behavior of the leakage current density J _A according to the content of erbium is shown in Fig. 5 (c). Behavior up the breakdown electric field (E _1mA) and a non-linear coefficient (a) as opposed to erbium (Er ₂ O ₃₎ showed the lowest level of 73 / cm ² when the content is 0.05 mol%, yielding an electric field (E _1mA) and When the nonlinear coefficient (a) shows the maximum value, the behavior in which the leakage current density (J _A ) shows the minimum value can be evaluated as a remarkably excellent characteristic.

5, it is preferable that erbium (Er ₂ O ₃ ) is added to the vanadium-based zinc oxide varistor of the present invention and the content thereof is adjusted to 0.1 mol% or less, more preferably 0.05 mol% It can be said that erbium (Er ₂ O ₃ ) is added.

As shown in the graph of FIG. 5, when the content of erbium (Er ₂ O ₃ ) is adjusted to 0.1 mol% or less, the vanadium-based zinc oxide varistor of the present invention has a breakdown field (E _{1 mA} ) of 5,000 V / cm or more, and the nonlinear coefficient (a) is 50 or more.

DC acceleration aging stress measurement

In order to evaluate the stability of the nonlinearity and electrical characteristics of the varistor, the DC accelerated aging stress test was performed under the condition of 0.85E _1mA / 85 / 24h after measuring the stress-applied voltage-current (EJ) characteristics for each specimen. _m

The leakage current (J _A ) was measured at 1 minute intervals during stress application using a high voltage source-measure unit (Keithley 237, Keithley Instruments Inc., Cleveland, OH, USA).

The degradation rate coefficient changes in the leakage current (J _L) according to stress time, while applying a stress (degradation rate coefficient, K _T) is _{I L = I L0 + K T} · t 1/2 ( Here, I _L is the time t is the leakage current at t, and I _L0 is the leakage current at t = 0).

FIG. 5 is a graph showing the behavior of leakage current (I _L ) of four specimens according to the progression of DC accelerated aging stress. It can be seen that each specimen exhibits a distinct behavior depending on the elapsed time of stress application.

The specimen (a) without erbium exhibits a considerable increase in leakage current (I _L ) as stress is applied, but does not exhibit thermal run-away phenomena.

The specimens (b) and (c) containing 0.05 and 0.1 mol% of erbium, respectively, showed that the leakage current (I _L ) remained almost constant even after the stress was applied and significantly improved compared to the specimen without erbium Respectively.

However, the specimen (d) containing 0.25 mol% of erbium caused thermal runaway soon after the stress was applied.

In general, low sintered density and high leakage current significantly reduce the stability of the varistor against stress. Electrons reduce the number of conduction paths and ultimately cause current concentration. Joule), which leads to repeated cycles between heat generation and leakage current, which reduces stability. From this point of view, it is considered that the sintered density of the entire specimen is almost the same, but the specimen (d) is relatively high in ErVO _{4, which} is the subcrystalline phase, so that the leakage current is too excessive and the stability is weakened in the overall result.

The stability of the varistor is evaluated to be better as the deterioration coefficient (K _T ), which is the slope of the leakage current change with the stress time, is better. The degradation coefficient (K _T ) for each specimen is summarized in Table 2 below.

Voltage-current (E-J) characteristics before and after DC accelerated aging stress on the four specimens of the present invention Psalter Stress condition K _T
(PA.h ^-1/2 ) E _1mA
(V / cm) % △ E _1mA alpha % △ α (a) Early - 4800 - 49.9 - 0.85E _1mA / 85 ° C / 24h 27.6 4389 -8.6 19.7 -60.5 (b) Early - 5444 - 63.4 - 0.85E _1mA / 85 ° C / 24h 16.3 5123 -5.9 29.1 -54.1 (c) Early - 5266 - 51.1 - 0.85E _1mA / 85 ° C / 24h 11.2 4875 -7.4 18.4 -64.0 (d) Early - 4061 - 14.8 - 0.85E _1mA / 85 ° C / 24h Heat runaway 2833 -30.2 4.4 -70.3

FIG. 6 shows voltage-current (EJ) characteristics before and after DC accelerated aging stress for specimens (a) to (d) with different contents of erbium, It can be confirmed that it has a great influence on the characteristic change.

The specimen (d) containing 0.25 mol% of erbium showed a large change in the voltage-current (EJ) characteristics before and after the stress application, while the specimen (b) containing 0.05 mol% showed the smallest change. This is consistent with the behavior of the leakage current (I _A ) of the four specimens as the DC accelerated aging stress of FIG. 5 progresses.

The values of the breakdown field (E _1mA ) and the nonlinear coefficient (a) before and after the application of other DC accelerated aging stresses and the rate of change (% E _1mA ,%) of each are summarized in Table 2 above. (B) containing 0.05 mol% of erbium in both the breakdown field (E _1mA ) and the nonlinear coefficient (a) showed the best results. The specimen (a) without erbium and the specimen ) Seems to be about the same level.

However, in the specimen (d), the breakdown field (E _1mA ) greatly decreased (-30.2%) after DC accelerated aging stress, and the nonlinear coefficient (a) It should be noted, however, that since the specimen (b) maintains a significantly higher nonlinear coefficient (a) of 29.1 as the absolute value after stressing, the performance as a varistor still remains good.

As described above, the vanadium-based zinc oxide varistor according to the present invention has excellent voltage-current (EJ) characteristics by controlling the content of erbium added in a small amount. Especially, when the content of erbium is 0.05 mol%, the non- High level.

In addition, the vanadium-based zinc oxide varistor of the present invention can control the content of erbium (Er ₂ O ₃ ), which is essentially added, to 0.1 mol% or less, more preferably 0.05 mol% ) Characteristics.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention . Therefore, the true scope of protection of the present invention should be determined by the claims.

Claims (9)

A vanadium-based zinc oxide varistor comprising zinc oxide (ZnO) as a main component and vanadium oxide (V ₂ O ₅ ), manganese oxide (MnO ₂ ) and niobium oxide (Nb ₂ O ₅ )
A vanadium-based zinc oxide varistor characterized in that erbium oxide (Er ₂ O ₃ ) is further added to the vanadium-based zinc oxide varistor. The method according to claim 1,
Wherein the erbium oxide (Er ₂ O ₃ ) is added in an amount of 0.1 mol% or less. 3. The method of claim 2,
Wherein the erbium oxide (Er ₂ O ₃ ) is added in an amount of 0.05 mol%. 3. The method of claim 2,
Wherein the vanadium-based zinc oxide varistor has a breakdown field (E _{1 mA} ) of 5,000 V / cm or more and a nonlinear coefficient (a) of 50 or more. 5. The method according to any one of claims 1 to 4,
The composition of the vanadium-based zinc oxide varistor is (97.4-X) mol% ZnO + 0.5 mol% V ₂ O ₅ + 2.0 mol% MnO ₂ + 0.1 mol% Nb ₂ O ₅ + X mol% Er ₂ O ₃ Based vanadium oxide zinc varistor. A first step of weighing zinc oxide (ZnO), vanadium oxide (V ₂ O ₅ ), manganese oxide (MnO ₂ ), niobium oxide (Nb ₂ O ₅ ) and erbium oxide (Er ₂ O ₃ );
A second step of adding acetone to the weighed composition and mixing by ball milling;
Mixing the mixture obtained through the second step in a container containing a polyvinyl butyral (PVB) binder and acetone, and drying the mixture;
A fourth step of making the mixed composition into a desired shape and sintering, and then polishing both surfaces of the sintered body; And
And a fifth step of applying a silver electrode to the polished sintered body and performing a package treatment. The method according to claim 6,
Wherein the erbium oxide (Er ₂ O ₃ ) is added in an amount of 0.1 mol% or less. 8. The method of claim 7,
Wherein the erbium oxide (Er ₂ O ₃ ) is added in an amount of 0.05 mol%. 9. The method according to any one of claims 6 to 8,
The composition of the vanadium-based zinc oxide varistor is (97.4-X) mol% ZnO + 0.5 mol% V ₂ O ₅ + 2.0 mol% MnO ₂ + 0.1 mol% Nb ₂ O ₅ + X mol% Er ₂ O ₃ By weight based on the total weight of the vanadium-based zinc oxide varistor.

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