• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.835-839
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• 2004

The surge characteristics of ZnO varistors consisting of $ZnO-{Pr}_6{O}_11-CoO-{Cr}_2{O}_3-{Er}_2{O}_3$ceramics were investigated at various sintering temperatures. As sintering temperature raises, the varistor voltage was decreased from 341.2 to 223.1 V/mm, the nonlinear exponent was decreased from 64,9 to 44.1. On the other hand, the leakage current exhibited a minimum(0.64 $\mu$A) at 134$0^{\circ}C$, The clamping capability was slightly deteriorated with increasing sintering temperature. On the whole, the ZPCCE-based ZnO varistors exhibited good clamping voltage characteristics as exhibiting the clamping voltage ratio of 1.85 ∼ 1.92 approximately at surge current of 100 A.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.933-938
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• 2002

(Ba,Sr)TiO$_{4}$ (BST) thin films on Pt/Ti/SiO$_{2}$/Si substrates were deposited by a sol-gel method and the etch characteristics of BST thin films have been investigated as a function of gas mixing ratio. The maximum etch rate of the BST films was 440 $AA$/min under such conditions as: CF$_{4}$(CF$_{4}$＋Ar) of 0.2, RF-power of 700 W, DC-bias voltage of -200 V, pressure of 15 mTorr and substrate temperature of 30 $^{circ}C$. The selectivities of BST to Pt, SiO$_{2}$ and PR were 0.38, 0.25 and 0.09, respectively. In the XPS (X-ray photoelectron spectroscopy) analysis, Barium (Ba) and Strontium (Sr) component in BST thin films formed low volatile compounds such as BaFx, SrFx, which are forms by the chemical reaction with F atoms and is removed by Ar ion bombardment. Titanium (Ti) is removed by chemical reaction such as TiF with ease. The result of secondary ion mass spectrometry (SIMS) analysis confirmed the existence of the BaFx, SrFK, TiFx.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1706-1708
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• 2004

This paper reports the stability against surge of ZnO-$Pr_6O_{11}$-CoO-$Cr_2O_3-Er_2O_3$-based varistors sintered at different sintering temperatures. As sintering temperature increases, the varistor voltage decreased in the range of 412${\sim}$266 V and the nonlinear exponent decreased in the range of 61${\sim}$50. Meanwhile, the stability against surge with surge peak current of 100 $A/cm^2(8{\times}20{\mu}s)$ exhibited to be good on the whole.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.472-475
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• 2001

The electrical properties and stability of ZPCCY-based varistors composing of $ZnO-Pr_{6}O_{11}-CoO-Cr_{2}O_{3}-Y_{2}O_{3}$ ceramics were investigated with sintering time. As sintering time is increased, the nonlinear exponent decreased in the range of 51.19~26.70. Among varistors having above 30 in nonlinear exponent, for the varistor sintered for 1h, the nonlinearity was superior to the stability comparatively and, in the case of 2h, the stability was superior to the nonlinearity relatively. Consequently, it is estimated that the varistors sintered for 1~2h will be applied to various fields by trade-off between nonlinearity and stability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.472-475
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• 2001

The electrical properties and stability of ZPCCY-based varistors composing of ZnO-Pr$_{6}$ O$_{11}$ -CoO-Cr$_2$O$_3$-Y$_2$O$_3$ ceramics were investigated with sintering time. As sintering time is increased, the nonlinear exponent decreased in the range of 51.19∼26.70. Among varistors having above 30 in nonlinear exponent, for the varistor sintered for 1h, the nonlinearity was superior to the stability comparatively and, in the case of 2h, the stability was superior to the nonlinearity relatively. Consequently, it is estimated that the varistors sintered for 1∼2h will be applied to various fields by trade-off between nonlinearity and stability.

• Transactions on Electrical and Electronic Materials
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• v.12 no.5
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• pp.213-217
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• 2011

The nonlinear electrical properties and degradation behavior against an impulse-current of 400 A in the ZnO-$Pr_6O_{11}$-CoO-$Cr_2O_3$-$Y_2O_3$-$Er_2O_3$ (ZPCCYE) varistors were investigated with different $Y_2O_3/Er_2O_3$ ratios. The $Y_2O_3/Er_2O_3$ mole ratio has a significant effect on nonlinear electrical properties and impulse degradation behavior of the ZPCCYE varistors. The varistors added with $Y_2O_3/Er_2O_3$ = 0.5/0.5 exhibited the best nonlinear properties with 39 in nonlinear coefficient (${\alpha}$) and the best clamp characteristics, in which the clamping voltage ratio (K) was in the range of K = 1.62-2.18 at an impulse-current of 1-50 A. The varistors added with $Y_2O_3/Er_2O_3$ = 0.25/0.5 exhibited the best electrical stability, with $%{\Delta}E_{1mA/cm^2}$=-5.6%, $%{\Delta}{\alpha}$ = 6.7%, and $%{\Delta}J_L$ = -14.6% against an impulse-current of 400 A. On the contrary, the varistors added with $Y_2O_3/Er_2O_3$ = 0.5/0.5 were destroyed applying an impulse-current of 400 A.

• Bulletin of the Korean Chemical Society
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• v.18 no.2
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• pp.218-221
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• 1997

When phenylation of styrene was carried out in the presence of Pd(OAc)2 and PPh3 in benzene, trans-stilbene was obtained in good yield (566%) with high selectivity (98%) under mild condition (55 ℃, 50 psi O2, 20 h). Since trans-stilbene could be produced not only from benzene but also from phenyl group of PPh3 by migration of its phenyl group to Pd, the competitiveness of benzene and the migratory aptitude of aryl group of triarylphosphine toward styrene has been investigated with various phosphines (PR3: P(p-C6H4CH3)3, P(p-C6H4OCH3)3, P(p-C6H4F)3, P(p-C6H4Cl)3, P(C6H5)3, P(C6H11)3, P(OC4H9n)3, P(CH2C6H5)3 and P(C6F5)3). The yield and selectivity toward trans-stilbene are increased as the basicity of the phosphines increases. The composition of arylated olefin from arylphosphine, in turn, increases as the electronegativity of the substituent on the aryl group of arylphosphines increases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.415-418
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• 2001

The I-V characteristics and its stability of ZPCCL-based ceramic varistors doped with La$_2$O$_3$in the range of 0.0~4.0 mol% were investigated. The density of ceramics was increased in the range of 4.7~5.8 g/cm$^3$ with increasing La$_2$O$_3$content. As La$_2$O$_3$content is increased, the varistor voltage was decreased in the range of 503.49-9.42 V/mm up to 2.0 mol%, whereas increasing La$_2$O$_3$content further caused it to increase. The ZPCCL-based varistors were characterized by nonlinearity, in which the nonlinear exponent is in the range of 3.05~82.43 and leakage current is in the range of 0.24-100.22 $\mu$A. Among ZPCCL-based varistors, 0.5 mol% added-varistors exhibited an excellent nonlinearity, in which the nonlinear exponent is 82.43 and the leakage current is 0.24 $\mu$A. Furthermore, they exhibited a high stability, in which the variation rate of the varistor voltage and the nonlinear exponent was -1.11% and -6.72%, respectively, under DC stress, such as (0.80 V$_{1mA}$9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$115$^{\circ}C$//12h) +(0.90 V$_{1mA}$12$0^{\circ}C$//12h)+(0.95 V$_{1mA}$1$25^{\circ}C$//12h)+(0.95 V$_{1mA}$15$0^{\circ}C$//12h). Consequently, it was estimated that ZPCCL-based ceramics will be applied to development of Pr$_{6}$O$_{11}$ based ZnO varistors having a high performance.e.rformance.e.

• Korean Journal of Materials Research
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• v.11 no.9
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• pp.769-775
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• 2001

High quality PZT piezoelectric thin films were sputter- deposited on$ RuO_2$/$SiO_2$/Si substrates by using 2-step deposition method. As the first step, PZT seed layers were fabricated at a low temperature($475^{\circ}C$ ) to form a pure perovskite phase by reducing the volatility of Pb oxide. and then, as the second step, the PZT films were deposited at high temperatures ($530^{\circ}C$~$570^{\circ}C$) to reduce the defect density in the films. By this method, the pure perovskite phase was obtained at high deposition temperature range ($530^{\circ}C$~$570^{\circ}C$) and the superior electrical properties of PZT films were obtained on $RuO_2$substrate : 2Pr : 60$\mu$C/$\textrm{cm}^2$, $E_c: 60kV/cm, \;J_t: 10^{-6}A/cm^2\; at\; 250kV/cm$. The residual stress of PZT films fabricated by the 2-step deposition method was tensile and below 150MPa. It was attempted to control the residual stress in the PZT films by applying a negative bias to the substrate. As the amplitude of the substrate bias was increased, the residual tensile stress was slightly decreased, however, the ferroelectric properties of PZT films were degraded by ion bombardment.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.490-496
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• 2005

The electrical properties and stability of the varistors composed of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_{2}$O$_{3}$-Dy$_{2}$O$_{3}$ system were investigated with sintering time in the range of 1$\~$3 h at 1350$^{\circ}C$ . As the sintering time was increased, the varistor voltage and leakage current increased, but the nonlinear exponent decreased. The varistors sintered for 1 h exhibited excellent nonlinearity, with a nonlinear exponent of 55.3 and a leakage current of 0.1 $\mu$A, whereas presented relatively low stability. The varistors sintered for 2 h exhibited not only high nonlinear exponent of 46.3, low leakage current of 0.3 $\mu$A, low dielectric dissipation factor of 0.0431, but also the highest stability, in which the variation rates of varistor voltage, nonlinear exponent, leakage current, dielectric constant, and dielectric dissipation factor were -3.0$\%$, -4.1$\%$, +3056.2$\%$, +5.1$\%$, and -12.5$\%$, respectively, after DC accelerated aging stress state of 0.95 V$_{1ma}$/150$^{\circ}C$/24 h. On the whole, the nonlinearity and stability of these varistors are greatly affected by the sintering time.