• 한국전기전자재료학회논문지
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• 제18권12호
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• pp.1111-1116
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• 2005

ZnO varistor ceramics added a glass-frit 0.03 $wt\%$ were fabricated with variation of sintering temperature. The sintering temperature and time were $1125^{\circ}C\~1200^{\circ}C$ and 2 h. The average grain sizes increased and the varistor voltage decreased with increasing the sintering temperature. The values of the specimen sintered at $1200^{\circ}C$ were $23.7\;{\mu}m$ and 329 V, respectively. The leakage current of all specimens was less than $1\;{\mu}A$ at DC $82\%$ of varistor voltage. The clamping voltage ratio of the specimen sintered at $1175^{\circ}C$ was 1.37. The endurance of surge current and the deviation of varistor voltage of the specimen sintered at $1175^{\circ}C$ were 6400 $A/cm^2$ and ${\Delta}-2.81\%$, respectively. After the High Temperature Load Test(HTLT) at $85^{\circ}C$ for 1000 h, the specimen sintered at $1175^{\circ}C$ showed the lowest deviation of varistor voltage of ${\Delta}-1.92\%$.

• 한국전기전자재료학회논문지
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• 제15권10호
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• pp.876-882
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• 2002

The microstructure and electrical characteristics of ZPCD (ZnO-$Pr_{6}O_{11}$-CoO-$Dy_2O_3$) -based varistor ceramics were investigated with various $Pr_{6}O_{11}$/CoO ratios and sintering temperatures. The density of varistor ceramics with $Pr_{6}O_{11}$=1.0 was almost constant with sintering temperature, whereas it was increased noticeably in $Pr_{6}O_{11}$=0.5. Increasing $Pr_{6}O_{11}$ content enhanced the densification for any CoO content and the density was greatly affected not by CoO content but by $Pr_{6}O_{11}$ content. The varistor ceramics with $Pr_{6}O_{11}$/CoO=0.5/l.0 exhibited a higher nonlinearity than any other composition ratios. In particular, the varistor ceramics sintered at $1350^{\circ}C$ exhibited the best electrical properties, with nonlinear exponent of 37.8, leakage current of 7.6 ${\mu}$A, and tan $\delta$ of 0.059.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.603-606
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• 2004

ZnO varistor ceramics were fabricated with variation of addition of $Nd_2O_3$ amount and the sintering temperature was $l150^{/circ}C$. The average grain sizes were showed decreased from $13.8{\mu}m$ to $4.7{\mu}m$, and varistor voltages were increased from 398 V to 657 V by added amount of $Nd_2O_3$. Nonlinear coefficient a of all were with increasing the amount of $Nd_2O_3$ more than 60, in case of added on 0.1mol% $Nd_2O_3$ was 87. And leakage current were less than $1_{\mu}A$ with applied at 82% of varistor voltage. The clamping voltage ratio of the specimes added 0.1mol% $Nd_2O_3$ was 1.38 at applied 25A [$8/20{\mu}s$]. In the specimen added 0.1mol% $Nd_2O_3$, endurence of surge current and deviation of varistor voltage were 7000A/$cm^2$, $\Delta-2.08%$, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.375-378
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• 2004

ZnO varistor ceramics were fabricated with variation of addition of glass-frit amount and the sintering temperature was $1150^{\circ}C$. The average grain sizes were showed decreased from $8.6\;{\mu}m$ to $10\;{\mu}m$, and varistor voltages were decreased from 506 V to 460 V by added amount of glass-frit. Nonlinear coefficient ${\alpha}$, of all were with increasing the amount of glass-frit more than 60, in case of added on 0.03wt% glass-frit was 83. And leakage current were less than $1{\mu}A$ with applied at 82% of varistor voltage. The clamping voltage ratio of the specimes added 0.03wt% glass-frit was 1.41 at applied 25A $[8/20{\mu}s]$. In the specimen added 0.03wt% glass-frit, endurence of surge current and deviation of varistor voltage were $6200A/cm^2$, $\Delta-1.67%$, respectively.

• 한국전기전자재료학회논문지
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• 제24권11호
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• pp.876-881
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• 2011

The sintering, defect and grain boundary characteristics of Bi-based ZnO chip varistor (1,608 mm size) have been investigated to know the possibility of lowering a manufacturing price by using 100 % Ag inner-electrode. The samples were prepared by general multilayer chip varistor process and characterized by shrinkage, SEM, current-voltage (I-V), admittance spectroscopy (AS), impedance and modulus spectroscopy (IS & MS) measurement. There are no problems to make a chip varistor with 100% Ag inner-electrode in the sintering temperature range of 850~900$^{\circ}C$ for 1 h in air. A good varistor characteristics ($V_n$= 9.3~15.4 V, a= 23~24, $I_L$= 1.0~1.6 ${\mu}A$) were revealed but formed $Zn_i^{{\cdot}{\cdot}}$(0.209 eV) as dominant defect, and increased the distributional inhomogeneity and the temperature instability in grain boundary barriers.

• 한국세라믹학회지
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• 제35권11호
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• pp.1121-1129
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• 1998

Reactions between Ag-Pd internal electrode materials and{{{{ { {Bi }_{2 }O }_{3 } }} in multilayer chip varistor were in-vestigated. For more than 1 mol%{{{{ { {Bi }_{2 }O }_{3 } }} in varistor composition internal electrode structure was destroyed due to the reaction between internal electrode and{{{{ { {Bi }_{2 }O }_{3 } }} But for typical varistor compositions (below 1 mol% of{{{{ { {Bi }_{2 }O }_{3 } }} content) microstructural changes around the internal electrode were not observed. However SEM-EDS and TEM-EDS analysis showed the uneven distribution of{{{{ { {Bi }_{2 }O }_{3 } }} in the internal electrode which was due to the migration of{{{{ { {Bi }_{2 }O }_{3 } }} to the electorde during sintering. As a results the nonlinear coefficient of multilayer varistor showed very large distribution as well as the breakdown voltage.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.307-308
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• 2005

ZnO varistor ceramics were fabricated as a function of the sintering temperature from $1125^{\circ}C$ to $1200^{\circ}C$ with glass-frit 0.03wt% addition. The average grain size was increased from 10.4 ${\mu}m$ to 23.7 ${\mu}m$, and varistor voltage was decreased from 538 V to 329 V with rising of the sintering temperature. The nonlinear coefficient a showed similar value from 75 to 80 and leakage current of all specimens exhibited the result of $1{\mu}A$ at 82% of varistor voltage. But the clamping voltage ratio of the specimens sintered at $1175^{\circ}C$ was 1.37 at 25A [$8/20{\mu}s$]. Also, endurance of surge current and deviation of varistor voltage of sintered specimens at $1175^{\circ}C$ were $6400A/cm^2$, $\Delta$-3.32%, respectively.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.489-494
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• 2001

In this thesis, the microstructure and electrical properties of ZnO varistors were investigated according to ZnO varistors with various formulation. A∼E's ZnO varistor ceramics were exhibited good density, 95% of theory density and low porosity, 5%, wholly. The average grain size of A-E's ZnO varistor ceramics exhibited 11.89$\mu\textrm{m}$, 13.57$\mu\textrm{m}$, 15.44$\mu\textrm{m}$, 11.92$\mu\textrm{m}$, 12.47$\mu\textrm{m}$, respectively. Grain size of C's ZnO varistor is larger and grain size of A and D's are smaller than other varistors. In the microstructure, A∼E's ZnO varistor ceramics sintered at l130$^{\circ}C$ was consisted of ZnO grain(ZnO), spinel phase(Zn$\sub$2.33/Sb$\sub$0.67/O$_4$), Bi-rich Phase(Bi$_2$O$_3$) and inergranular phase, wholly. Reference voltage of A∼E's ZnO varistor sintered at 1130$^{\circ}C$ decreased in order D, E > A > B > C's ZnO varistors. Nonlinear exponent of varistors exhibited high characteristics, above 30, wholly. Consequently, C's ZnO varistor exhibited good nonlinear exponent, 68. Lightning impulse residual voltage of A, B, C and E's ZnO varistors suited standard characteristics, below 12kV at current of 5kA.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.705-709
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• 2003

The microstructure and electrical properties of the $Pr_6O_{11}$-based ZnO varistor ceramics, which are composed of Zn-Pr-Co-Cr-Tb oxides, were investigated with $Tb_4O_7$ amount. The varistor ceramics exhibited very high densification based on increasing density in the range of $5.73{\sim}5.85g/cm^3$ as $Tb_4O_7$ amount is increased. The calculated nonlinear exponent( ${\alpha}$ ) in varistor ceramics without $Tb_4O_7$ was only 8.9, whereas the ${\alpha}$ value of the varistor ceramics with $Tb_4O_7$ was abruptly increased in the range of 18.6 to 42.0. In particular, the maximum value(42.0) of ${\alpha}$ was obtained by doping of 1.0 mol% $Tb_4O_7$. The measured leakage current($I_{\ell}$) in varistor ceramics without $Tb_4O_7$ was $40.1{\mu}A$, whereas the $I{\ell}$ value of the varistors with $Tb_4O_7$ was very abruptly decreased below $5{\mu}A$. It is estimated that $Tb_4O_7$ additives will is applied usefully in development of varistors possessing high performance.

• 한국전기전자재료학회논문지
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• 제11권1호
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• pp.48-56
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• 1998

Pr\ulcornerO\ulcorner-based ZnO varistors were fabricated in the range of $Y_2$O$_3$additive content from 0.5 to 4.0mol%, and its microstructure and electrical properties were investigated. Yttrium was distributed nearly in the grain boundaries and the cluster phase formed at nodal point but more in cluster phase. The average grain size was decreased markedly from 34.9 to 8.6${\mu}{\textrm}{m}$ with increasing $Y_2$O$_3$additive content. It is believed that the decrease of grain size is attributed to the formation of cluster phase and the weakening of driving force for liquid sintering. As a result, $Y_2$O$_3$was acted as the inhibitor of the grain growth. With increasing $Y_2$O$_3$additive content, the varistor voltage, the activation energy, and the nonlinear exponent increased whereas the leakage current decreased, especially 4.0mol% $Y_2$O$_3$-added varistor exhibited very good I-V characteristics; nonlinear exponent 87.42 and leakage current 46.77nA. On the other hand, as $Y_2$O$_3$additive content increases, the varistor showed tendency of the salient decrease for donor concentration and the increase for barrier height. Conclusively, it is estimated that ZnO:Pr varistor compositions added more than 2.0mol% $Y_2$O$_3$are to be used to fabricate useful varistors.