KR102137485B1 - Vanadia-based zinc oxide varistors doped with yttria and maunfacturing method for the same - Google Patents

Abstract

The present invention relates to a zinc oxide-vanadia varistor with yttria added, which shows a very high resistance value below a breakdown voltage but shows a low resistance value above the breakdown voltage, and which has excellent nonlinear properties at a specific amount of yttria added and exhibits high interfacial state density and high potential barrier height; and a manufacturing method thereof. In addition, the present invention relates to the zinc oxide-vanadia varistor with yttria added and the manufacturing method thereof, which can act as a donor based on a chemical defect reaction. The present invention can provide a chip varistor using the zinc oxide-vanadia varistor with yttria added.

Description

Zinc Oxide-Vanadia Varistor with Yttria added and its manufacturing method{VANADIA-BASED ZINC OXIDE VARISTORS DOPED WITH YTTRIA AND MAUNFACTURING METHOD FOR THE SAME}

The present invention relates to a zinc oxide-vanadia-based varistor to which yttria is added and a method for manufacturing the same, more specifically, a zinc oxide varistor that protects electronic circuit components used in electronic devices from surges and abnormal voltages, and It relates to a manufacturing method.

A varistor is a device used to protect electronic circuits and components used in electronic devices such as portable terminals from abnormal voltages such as surge and pulsed noise, which are electronic circuits and components against the generation of static electricity. It ensures effective protection against noise regulation while ensuring the protection and operational stability of the system.

For example, LED TV. Smartphones, cameras, and PCs can be very sensitive and vulnerable to surges, which are transient waveforms of current, voltage, and power in electrical and electronic circuits. At this time, 60 to 80% of surges are generated inside the facility, and in semiconductor devices, surges can be said to cause significant damage.

The varistor may mean a voltage-dependent resistor or a nonlinear resistor. The resistance of the varistor changes with the applied voltage, unlike the normal resistance. Therefore, the material exhibiting the varistor effect must have a microstructure such as pn junction or active particle boundary or active interface.

On the other hand, zinc oxide varistors containing zinc oxide (zinc oxide varistor) can be prepared by firing at an appropriate temperature by adding some additives to the zinc oxide. The microstructure of the doped zinc oxide varistor is a polycrystalline structure composed of numerous semiconducting zinc oxide particles and grain boundaries. The grain is a semiconductor with a bandgap of about 3.2 eV, and the grain boundary is active against electrons and has a very thin insulating layer. As a result, one semiconductor-insulating layer-semiconductor (SIS) structure constitutes a micro varistor, which is distributed randomly through the sintered body.

Thus, sintering zinc oxide doped with a specific additive can produce microstructures and nonlinear properties that are unique in conduction properties. Due to its excellent nonlinearity, zinc oxide varistors can be effectively applied to bypass electrical equipment from various passive and active devices, electrical and electronic equipment from dangerous transient voltages, and lightning.

Most varistors today are doped with several impurities, but bismuth is essentially doped, and in special cases praseodymium is doped. Since such varistor ceramics must be fired at a temperature higher than 1000°C, expensive Pd or Pt is inevitably used in the case of a multilayer type.

However, it may be desirable to use Ag having excellent conductivity as an internal electrode. At this time, a varistor ceramic capable of simultaneously firing at a temperature lower than the melting point of Ag is required. Therefore, zinc oxide ceramics doped with vanadium may be suitable for this. Since 1994, zinc oxide varistors doped with vanadium have been studied continuously, but the effect has not been satisfactory to date.

(Patent Document 1) KR 10-1948718 B1

An object of the present invention is to provide a zinc oxide-vanadia-based varistor to which yttria is added and a method for manufacturing the same.

Another object of the present invention is to show a very high resistance value below the breakdown voltage, but above it, it has excellent non-linear characteristics showing low resistance value, high interface state density and potential barrier height value, and improved stability and reliability. It is to provide a zinc oxide-vanadia-based varistor to which yttria is added and a method for manufacturing the same.

Another object of the present invention is to provide a zinc oxide-vanadia-based varistor added with yttria, which can act as a donor based on a chemical-defect reaction, and a method for manufacturing the same.

Another object of the present invention is to provide a chip varistor using the yttria-added zinc oxide-vanadia-based varistor.

To achieve the above object, a zinc oxide-vanadia-based varistor to which yttria is added according to an embodiment of the present invention includes zinc oxide (ZnO), vanadium oxide (vanadia, V ₂ O ₅ ), manganese oxide (MnO) ₂ ) and niobium oxide (Nb ₂ O ₅ ), and yttrium oxide (yttria, Y ₂ O ₃ ) may be additionally added.

The varistor comprises (97.4-x) mol% ZnO, 0.5 mol% V ₂ O ₅ , 2.0 mol% MnO ₂ , 0.1 mol% Nb ₂ O ₅ and x mol% Y ₂ O ₃ , where x is 0.05 to 0.05 0.25.

The varistor has a nonlinear index (α) of 40 to 67.

The interface state density (N _t ) of the varistor is 2.01×10 ₁₂ to 2.30×10 ¹² cm ^-2 , and the barrier height Φ _b is 0.77 to 1.24 eV.

The varistor has a donor concentration of 4.53 x 10 ¹⁷ cm ^-3 to 5.56 x 10 ¹⁷ cm ^-3 .

The varistor may act as a donor based on a chemical-defect reaction.

The chip varistor according to another embodiment of the present invention may be modularized by stacking a plurality of vanadia-based zinc oxide varistors to which the yttria is added, and a silver (Ag) internal electrode may be simultaneously formed therein.

The thin film according to another embodiment of the present invention includes a vanadia-based zinc oxide varistor to which the yttria is added.

Method for manufacturing a zinc oxide-vanadia-based varistor to which yttria is added according to another embodiment of the present invention is 1) zinc oxide (ZnO), vanadium oxide (vanadia, V ₂ O ₅ ), manganese oxide (MnO ₂ ), niobium oxide (Nb ₂ O ₅ ) and yttrium oxide (yttria, Y ₂ O ₃ ); 2) the weighed composition is ball milled to make a first mixture; 3) drying the first mixture; 4) preparing the second mixture by mixing and stirring the dried first mixture with acetone and a polyvinyl butyral binder; 5) preparing the starting powder by sieving the second mixture after drying; And 6) compressing the starting powder into pellets, and sintering and cooling to make a sintered body.

The varistor comprises (97.4-x) mol% ZnO, 0.5 mol% V ₂ O ₅ , 2.0 mol% MnO ₂ , 0.1 mol% Nb ₂ O ₅ and x mol% Y ₂ O ₃ , where x is 0.05 to 0.05 0.25.

Hereinafter, the present invention will be described in more detail.

The microstructure of a zinc oxide varistor sintered with a metal oxide as an additive includes polycrystalline zinc oxide particles and a grain boundary phase between the particles. Zinc oxide varistors exhibit excellent voltage-dependent characteristics, and this phenomenon is called a varistor effect. That is, the grains of zinc oxide have a very high electrical conductivity, while other oxides forming a grain boundary have a very large resistance. The electrical properties of the metal oxide varistors can be expressed as numerous fine varistors connected in series or in parallel.

For example, increasing the thickness of the varistor increases the breakdown voltage. This is the same as if the fine varistors are connected in series.

In addition, if the area of the varistor is increased, the surge current tolerance increases. This is the same as if the fine varistors are connected in parallel to each other.

In addition, if the volume of the varistor is doubled, the amount of energy is almost doubled. This is because the number of zinc oxide particles absorbing energy doubles.

The distribution of the zinc oxide particle size in the microstructure is very important in determining the breakdown voltage of the zinc oxide varistor. That is, the voltage of the varistor changes with the series number of grain boundaries, and the surge withstand voltage changes with the parallel number of grain boundaries.

Zinc oxide varistors are affected by particle growth depending on starting materials and sintering conditions. Zinc oxide varistors with oxide additives dominate the liquid phase sintering mechanism rather than solid phase sintering, so the content and distribution of the additives affect the particle size and distribution of the sintered body.

In the present invention, it is intended to provide a zinc oxide varistor with improved non-linear properties, despite no significant difference between before and after doping of the additives on the grain size and grain boundary distribution of the varistor.

More specifically, the zinc oxide-vanadia-based varistor to which yttria is added according to an embodiment of the present invention includes zinc oxide (ZnO), vanadium oxide (V ₂ O ₅ ), manganese oxide (MnO ₂ ), and niobium oxide ( Nb ₂ O ₅ ), and it characterized in that yttria (Y ₂ O ₃ ) is additionally added as an additive.

In the production of the varistor, the sintering density and the average particle size change are not large when the varistor is manufactured, as it is not added and as the content range is increased when added. That is, it was confirmed that the doping of yttrium does not significantly affect the microstructure.

The varistor comprises (97.4-x) mol% ZnO, 0.5 mol% V ₂ O ₅ , 2.0 mol% MnO ₂ , 0.1 mol% Nb ₂ O ₅ and x mol% Y ₂ O ₃ , where x is 0.05 to 0.05 0.25, preferably x is 0.05.

As described above, by adding a small amount of yttria, without affecting the sintering density and the average particle size, exhibiting excellent nonlinearity, it is possible to provide a varistor with improved stability and reliability.

Basically, the potential barrier is affected by various defects (additional defects such as intrusive zinc, interstitial oxygen, and zinc defects) at grain boundaries. Therefore, it will be said that the nonlinear index a of the varistor is greatly influenced by the Schottky barrier.

In the production of the varistor of the present invention, as a small amount of yttria is added, YVO ₄ is formed in the minor phase, and the nonlinear index is affected by the content of the minor phase. That is, YVO ₄ with or without YVO ₄ may reduce the nonlinear index a.

It will be said that when yttria is added only within the content range of the present invention, a suitable minor phase YVO ₄ is formed, and thus an optimal nonlinear index value can be exhibited.

Leakage current density (J _L ) and breakdown field (E _{1 mA/cm} ² ) increase as the doping content of yttria increases, but in the case of a nonlinear index, the 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 and x mol% Y ₂ O ₃ , wherein x represents a maximum value when 0.05.

The non-linear index (α) of the varistor is 40 to 67, but preferably, Y ₂ O ₃ has a maximum value of 0.05 mol% to 67.

A large nonlinear index means that the resistance value is very high below the breakdown voltage, but above it means that the resistance value is low, and through this, it is possible to absorb and extinguish the external sudden voltage rise by itself. . By absorbing the surge voltage, the electronic circuit components can be protected from surge and abnormal voltage.

The interface state density (N _t ) of the varistor is 2.01×10 ¹² to 2.30×10 ¹² cm ^-2 , and the barrier height Φ _b is 0.77 to 1.24 eV.

Preferably, the interface state density (N _t ) of the varistor is 2.30×10 ¹² cm ^-2 and the barrier height Φ _b is 1.24 eV.

The tendency of interstate density and dislocation barrier height to coincide with the degree of doping of yttria is consistent. It will be said that the higher the interfacial state density and the potential barrier height value, the better the nonlinear characteristics.

The varistor of the present invention has a donor concentration of 4.53 × 10 ¹⁷ cm ^-3 to 5.56 × 10 ¹⁷ cm ^-3 , and preferably 4.53 × 10 ¹⁷ cm ^-3 as the yttria is further added. Yttrium dopants can act as donors based on the following chemical-defect reactions:

[Reaction formula]

A method of manufacturing a zinc oxide-vadiadia varistor to which yttria is added according to another embodiment of the present invention is 1) zinc oxide (ZnO), vanadium oxide (vanadia, V ₂ O ₅ ), manganese oxide (MnO ₂ ), niobium oxide (Nb ₂ O ₅ ) and yttrium oxide (yttria, Y ₂ O ₃ ); 2) the weighed composition is mixed with acetone and ball milled to make a mixture; 3) drying the mixture; 4) preparing the granulated powder by granulating the dried mixture with a polyvinyl butyral binder; 5) pressing the granule powder to sinter into a disk shape; And 6) sintering.

The composition ratio of the 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 and x mol% Y ₂ O ₃ , and x is 0.05 to 0.05 0.25, preferably x is 0.05.

More specifically, step 1) is for preparing a composition within the scope of the present invention by weighing a component for preparing a zinc oxide-vanadia-based varistor to which the yttria of the present invention is added.

When the weighing for the components in step 1) is completed, mix with acetone and ball mill to prepare a mixture. Through ball milling, the ceramic raw material is pulverized into fine powders, and uniformly mixed.

After preparing the mixture, it was dried at 120°C. The dried mixture was granulated with a polyvinyl butyral binder to prepare granular powder.

The granulated powder was compressed into a disk shape under pressure and sintered.

Thereafter, a silver electrode is applied to both surfaces of the sintered body, the lead wire is soldered, and then packaged to prepare a vanadia-based zinc oxide varistor.

According to the present invention, the zinc oxide-vanadia-based varistor to which yttria is added, and a method for manufacturing the same, exhibits a very high resistance value below the breakdown voltage, but more excellent nonlinear characteristics showing a low resistance value above, It shows the interface density and potential barrier height, improving stability and reliability.

In addition, it can act as a donor based on a chemical defect reaction.

The present invention can provide a chip varistor using the zinc oxide-vanadia-based varistor to which the yttria is added.

Figure 1 shows the surface microstructure of a specimen doped with yttria, wherein (a) 0.0 mol %, (b) 0.05 mol %, (c) 0.1 mol% and (d) 0.25 mol% of yttria are shown. SEM photograph of the added specimen.
Figure 2 shows the average grain size and sintering density of the specimen according to the content of yttria.
Figure 3 shows the XRD pattern of the specimen doped with yttria, (a) 0.0 mol%, (b) 0.05 mol%, (c) 0.1 mol% and (d) 0.25 mol% of yttria added XRD pattern of the specimen.
Figure 4 shows the JE properties of the specimen doped with yttria.
FIG. 5 shows the nonlinear index (a) and leakage current density of the ETRI-doped specimen.
6 shows CV characteristics of a specimen doped with yttria.
Figure 7 shows the dielectric properties of a specimen doped with yttria, (a) dielectric constant (ε _APP ') and (b) loss coefficient (tand).
8 shows the dielectric constant and dissipation factor of the ETRI-doped specimen.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

Preparation of yttria-added zinc oxide-vanadia varistor

Zinc oxide (ZnO), vanadium oxide (V ₂ O ₅ ), manganese oxide (MnO ₂ ), niobium oxide (Nb ₂ O ₅ ) and yttria (Y ₂ O ₃ ) were weighed.

The weighed raw powder was ball milled with acetone for 24 hours to produce a mixture, and the mixture was dried at 120°C. The dried mixture was granulated with a polyvinyl butyral (PVB) binder to prepare granular powder.

The granulated powder was compressed into a disk having a diameter of 10 mm and a thickness of 1.5 mm by applying a pressure of 1000 kg/cm ² .

After compression in the form of a disc, it was sintered for 3 hours at 900° C. on a magnesia plate. The final disc shape was wrapped and polished to a diameter of 8 mm and a thickness of 1.0 mm. An adhesive was applied to one surface of the conductive silver, and then adhered to the surface of the disc, followed by heating at 550° C. for 10 minutes.

The raw powder 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 and x mol% Y ₂ O ₃ , wherein x is 0, 0.05 , 0.1 and 0.25.

Microstructure characteristics

Microstructure images were taken using FESEM (Quanta 200).

The average grain size d was calculated by the following equation.

[Equation 1]

d = 1.56 L/MN

Where L is the random line length of the micrograph, M is the magnification of the micrograph, and N is the number of grain boundaries crossed by the line.

The crystal phase was confirmed by an X-ray diffractometer (XRD, Xpertpert-PRO MPD, Panalytical, Almelo, Netherlands) by CuK _α radiation. The density (ρ) of the sintered pellets was measured using a density determination kit (238490) attached to an electronic balance (AG 245, Mettler Toledo International Inc., Switzerland).

Figure 1 shows the surface microstructure of the ETRI-I doped specimen, (a) 0.0 mol%, (b) 0.05 mol%, (c) 0.1 mol% and (d) 0.25 mol% yttria content This is a SEM micrograph of the added specimen, Figure 2 shows the average grain size and sintered density of the specimen for the content of yttria.

There is no apparent difference in the surface of the test specimen without the yttrieye and the test specimen containing the yttria. The distribution of crystal phase was also homogeneous throughout. The average grain size d according to the yttria content is shown in FIG. 2.

As the yttria content increased, the average grain size d decreased slightly from 5.5 μm to 5.2 μm until the yttria content reached 0.1 mol %. When the yttria content exceeded 0.1 m ol%, the average particle (d) increased to 5.3 μm.

Looking at the results, it will be said that the change in the average grain size d according to the content of yttria is not large. The decrease in the average grain size d is due to the increase in YVO ₄ produced by doping yttria.

The sintering density ρ according to the content of yttria is shown in FIG. 2.

The sintering density (r) decreased to 0.05 mol%, and as the content of yttria increased, the sintering density (ρ) increased from 5.47 g/cm ³ to 5.51 g/cm ³ .

The change in sintering density (ρ) with increasing yttria content is also not as large as the average grain size (d).

Overall, the effect of yttria doping on the microstructure is not significant compared to other additives. The microstructure parameters according to the difference in yttria content are shown in Table 1 below.

Table 1 below shows the microstructure and electrical property parameters of the yttria-doped specimen.

Yttria content
(mol%) d
(μm) ρ
(g/cm ³ ) E _{1 mA/cm} ²
(V/cm) v _gb
(V/gb) a J _L
(μA/cm ² ) 0.0 5.5 5.50 4874 2.7 51 56.8 0.05 5.4 5.47 4989 2.7 67 99.7 0.1 5.2 5.49 5387 2.8 53 105.5 0.25 5.3 5.51 5355 2.8 40 251.6

Figure 3 shows the XRD pattern of the specimen doped with yttria, the content of yttria of (a) 0.0 mol %, (b) 0.05 mol %, (c) 0.1 mol% and (d) 0.25 mol %, respectively. XRD pattern of the added specimen.

All specimens formed a minor phase such as VO ₂ , ZnV ₂ O ₄ , and Zn ₃ (VO ₄ ) ₂ . The specimen doped with yttria formed YVO ₄ as a secondary phase.

Electrical properties

The current-voltage (I-V) characteristic was automatically measured using a high voltage SMU (Keithley 237).

The IV characteristic is converted into a current density-electric field (JE) characteristic. The breakdown voltage (V _{1 mA/cm} ² ) was measured at 1.0 mA/cm ² .

Leakage current (I _L ) was measured at 0.8 times V _{1 mA/cm} ² .

E _{1 mA/cm} ² = V _{1 mA/cm} ² /D

a = 1/log(V _{10 mA/cm} ² / V _{1 mA/cm} ² )

I _L /S

Calculate the breakdown field E _{1 mA/cm} ² , the nonlinear index a and the leakage current density J _L from the equation.

Where D is the thickness of the specimen (1mm), S is the area of the electrode.

Capacitance-voltage (C-V) characteristics were measured using a precision LCR meter (QuadTech 7600) and an electrometer (Keithley 617) under a bias voltage ranging from 0 to 100 V at a frequency of 1 kHz at a DC source.

The donor concentration (N _d ) and barrier height (Φ _b ) were determined by the following equation.

[Equation 2]

(1/C _b -1/2C _bo ) ² = 2(Φ _b + V _gb )/qεN _d

The interface state density (N _t ) at grain boundaries and grain boundaries was calculated by the following equation.

[Equation 3]

N _t = (2εN _d Φ _b /q) ^1/2

The apparent capacitance (C _APP ') and loss factor (tanδ) were measured at 10 Hz to 1 MHz using an RLC meter (QuadTech 7600).

The dielectric constant (ε _APP ') was calculated by the following equation.

[Equation 4]

C _APP '= ε _APP 'S/D

FIG. 4 shows the J-E characteristics of specimens doped with various yttria contents, and FIG. 5 shows the nonlinear index (a) and leakage current density of specimens with respect to the yttria content.

The J-E characteristic consists of an impedance region higher than the threshold voltage and an impedance region lower than the threshold voltage.

The distribution of the JE curve shows that yttria doping significantly affects the nonlinear properties. As the yttria content increased, the breakdown voltage area (E _{1 mA/cm} ² ) increased from 4874 V/cm to 5387 V/tsu until the yttria content reached 0.1 mol%.

When the yttria content exceeds 0.1 mol%, the E _{1 mA/cm} ² decreases to 5355 V/cm in 0.25 mol% yttria. As the yttria content increased, the behavior of E _{1 mA/cm} ² depended on the average grain size d.

Therefore, a decrease in the average grain size resulted in an increase in the number of grain boundaries. All specimens exhibited v _gb = 2.7 V/gb to 2.8 V/gb at breakdown voltage per grain boundary regardless of yttria content.

The nonlinear index a according to the yttria content is shown in FIG. 5. The J-E curve of the varistor ceramic is indicated by the nonlinear index a.

As the yttria content increased, the nonlinear index a increased significantly from 51 to 67 until the yttria content reached 0.05 mol%. When the content of yttria exceeds 0.05 mol%, the nonlinear index decreases to 40 in 0.25 mol% of yttria.

Specimens doped with 0.05 mol% yttria showed the largest a (a = 67) in the ZnO-V ₂ O ₅ system.

This is due to the decrease in the dislocation barrier height at the grain boundary, where the sharp decrease in the nonlinear index a with the addition of 0.25 mol% yttria.

Basically, the potential barrier is influenced by various defects (additional defects such as interstitial zinc, interstitial oxygen, and zinc defects) at the grain boundaries, and the nonlinear index a is greatly influenced by the Schottky barrier.

The behavior of the nonlinear index a depending on the content of yttria can be linked to the YbVO ₄ content. That is, YVO ₄ with or without YVO ₄ may reduce the nonlinear index a.

Leakage current density (J _L ) according to the amount of yttria is shown in FIG. 5.

With increasing amount of yttria, the leakage current density (J _L) is increased from 56.8μA / cm ² to 251.6 μA / cm ^2.

J-E characteristic parameters are shown in Table 1 above. According to the results in Table 1, yttria doping has a greater effect on J-E properties than microstructures.

Figure 6 shows the capacitance-voltage (C-V) characteristics of the yttria-added specimen. C-V characteristic parameters according to the content of yttria are shown in Table 1 above.

와 같은 화학적 결함(chemical-defect) 반응에 기초하여 도너(donor)로 작용한다.As the yttria content increased, the donor concentration increased from 2.46 × 10 ¹⁷ cm ^-3 to 5.56 × 10 ¹⁷ cm ^-3 . Yttrium dopant

Based on a chemical-defect reaction such as acts as a donor.

As the yttria content increased, the barrier height (Φ _b ) increased from 1.01 to 1.24 eV until the yttria content reached 0.05 mol%.

When the yttria content exceeded 0.05 mol%, Φ _b decreased to 0.77 eV.

The tendency of change in Φ _b was consistent with the tendency of the nonlinear index in JE properties as the yttria content increased.

In general, the higher the Φ _b , the better the nonlinearity.

On the other hand, the tendency to change the interface state density (N _t ) was consistent with the tendency of Φ _b according to the yttria content. This is because the barrier height is closely related to the density of the interfacial state.

Figure 7 shows the dielectric properties of the yttria-doped specimen, (a) is the dielectric constant (ε _APP '), (b) is the loss factor (tand). 8 shows the dielectric constant and dissipation factor of the sample for the yttria content.

Referring to FIG. 7 (a), when the frequency increases, the dielectric constant (ε _APP ') rapidly decreases below 1 kHz and gradually decreases above 100 kHz. As shown in FIG. 7, the influence of dielectric constant (ε _APP ') due to doping of yttria is not large compared to other characteristics.

The behavior of the dielectric constant (ε _APP ', 1 kHz) according to the amount of yttria is shown in FIG. 8. As the yttria content increased, the dielectric constant (ε _APP ', 1 kHz) decreased from 592.7 to 549.1 until the yttria content reached 0.1 mol%.

The dielectric constant (ε _APP ') increased to 568.6 at 0.25 mol%, when the yttria content was more than 0.1 mol%. The tendency to change the dielectric constant (ε _APP ') is related to the microstructure.

On the other hand, as shown in Fig. 7 (b), the loss coefficient (tanδ) in all samples rapidly decreased to about 20 kHz. All specimens showed absorption peaks at about 300 kHz, and decreased again when the frequency exceeded 300 kHz.

The tendency of change of the dissipation factor (tanδ, 1 kHz) according to the amount of yttria is shown in FIG. 8.

The loss coefficient (tanδ) increased from 0.209 to 0.313 as the amount of yttria increased. The tendency to change the loss factor (tanδ) is closely related to the leakage current.

On the other hand, the high loss factor (tanδ) in all samples is due to the relatively high leakage current. Dielectric parameters according to the content of yttria are shown in Table 2 below.

Specifically, Table 2 shows dielectric property parameters of specimens doped with C-V and various yttria contents.

Yttria content
(mol%) N _d
(10 ¹⁷ cm ^-3 ) Φ _b
(eV) N _t
(10 ¹² cm ^-2 ) ε _APP ''
(1 kHz) tand
(1 kHz) 0.0 2.46 1.01 1.53 592.7 0.209 0.05 4.53 1.24 2.30 559.8 0.233 0.1 5.18 1.03 2.23 549.1 0.248 0.25 5.56 0.77 2.01 568.6 0.313

In the present invention, the varistor properties of zinc oxide-vanadia-based ceramics by adding yttrium of 0 to 0.25 mol% were comprehensively confirmed.

The effect of yttria doping on the microstructure of varistor ceramics was not significant compared to other additives.

Specifically, the average grain size was changed in a narrow range of 5.2 μm to 5.5 μm, and the sintering density was changed in a narrow range of 5.47 g/cm ³ to 5.51 g/cm ³ .

However, the nonlinear properties showed a great effect despite small changes in yttria content.

For non-linear properties, it was confirmed that the most significant effect was obtained when 0.05 mol% of yttria was added.

In addition, when yttria is added, in view of an increase in electron concentration, it is expected that it can serve as a donor. Therefore, within the same content range as the present invention, yttria-doped zinc oxide-vanadia-based varistors will be utilized in various aspects.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (10)

Zinc oxide (ZnO) (97.4-x) mol%, vanadium oxide (V ₂ O ₅ ) 0.5 mol%, manganese oxide (MnO ₂ ) 2.0 mol% and niobium oxide (Nb ₂ O ₅ ) 0.1 mol%,
x mol% of yttria (Y ₂ O ₃ ) is additionally added,
YV0 ₄ is a minor phase (Minor phase) formed by the addition of the yttria,
The x is 0.05 to 0.25,
The nonlinear index (α) is 40 to 67
Zinc oxide-vanadia varistor with yttria added. delete delete According to claim 1,
The interface state density (N _t ) of the varistor is 2.01×10 ₁₂ to 2.30×10 ¹² cm ^-2 ,
The potential barrier height (Φ _b ) is 0.77 to 1.24 eV
Zinc oxide-vanadia varistor with yttria added. According to claim 1,
The varistor has a donor concentration of 4.53 × 10 ¹⁷ cm ^-3 to 5.56 × 10 ¹⁷ cm ^-3 .
Zinc oxide-vanadia varistor with yttria added. According to claim 1,
The varistor acts as a donor based on a chemical-defect reaction.
Zinc oxide-vanadia varistor with yttria added. According to paragraph 1 A number of zinc oxide-vanadia-based varistors with yttria added are stacked and modularized, and a silver (Ag) internal electrode is formed by co-firing.
Chip varistor. According to paragraph 1 Zinc oxide-vanadia varistor containing yttria
pellicle. 1) Weighing zinc oxide (ZnO), vanadium oxide (V ₂ O ₅ ), manganese oxide (MnO ₂ ), niobium oxide (Nb ₂ O ₅ ) and yttria (Y ₂ O ₃ );
2) the weighed composition is mixed with acetone and ball milled to make a mixture;
3) drying the mixture;
4) preparing the granulated powder by granulating the dried mixture with a polyvinyl butyral binder; And
5) pressing the granule powder to sinter into a disc shape
In the method of producing a zinc oxide-vanadia-based varistor to which yttria is added,
In step 1), zinc oxide (ZnO) (97.4-x) mol%, vanadium oxide (V ₂ O ₅ ) 0.5 mol%, manganese oxide (MnO ₂ ) 2.0 mol% and niobium oxide (Nb ₂ O ₅ ) 0.1 mol %,
x mol% of yttria (Y ₂ O ₃ ) is additionally added,
YV0 ₄ that is a minor phase (Minor phase) formed due to the addition of the yttri,
The x is 0.05 to 0.25,
The yttria-added zinc oxide-vanadia-based varistor prepared by the above step has a nonlinear index (α) of 40 to 67
Method for manufacturing zinc oxide-vanadia varistor to which yttria is added.
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