• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.22 no.1
• /
• pp.22-28
• /
• 2009

We investigated the sintering and electric properties of ZnO-1.0 at% $TeO_2$ (ZT1) and 1.0 at% Mn-doped ZT1(ZT1M1) system. $TeO_2$ itself melts at $732^{\circ}C$ in air but forms the $ZnTeO_3$ or $Zn_2Te_3O_8$ phase with ZnO as increasing temperature and therefore retards the densification of ZnO to $1000^{\circ}C$. In ZT1M1 system, also, the densification of ZnO was retarded up to $1000^{\circ}C$ and then reached > 90% of theoretical density above $1100^{\circ}C$. It was found that a good varistor characteristics(nonlinear coefficient $a{\sim}60$) were developed in ZT1M1 system sintered at $1100^{\circ}C$ due to Mn which known as improving the nonlinearity of ZnO varistors. The results of C-V characteristics such as barrier height (${\Phi}_b$), donor density ($N_D$), depletion layer (W), and interface state density ($N_t$) in ZT1M1 ceramics were $1.8{\times}10^{17}cm^{-3}$, 1.6 V, 93 nm, and $1.7{\times}10^{12}cm^{-2}$, respectively. Also we measured the resistance and capacitance of grain boundaries with temperature using impedance and electric modulus spectroscopy. It will be discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z(T)"-logf plots.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.30 no.4
• /
• pp.436-441
• /
• 1985

The study was conducted to provide basic information to breeders and agronomists working with sesame. The grain weight and germinability were investigated for eight plant types classified by branching habit, capsules per axil, and carpels and loculi of a capsule. Two typical cultivars were chosen for each plant type among 527 gene pools. Dry weight of one thousand grains was increased rapidly from 25th to 35th day after flowering, and reached peak on 40th day after flowering in upper part capsules and 45th day after flowering in lower and middle part capsules, so that this period was considered to be of physiological maturity in each capsule bearing part. Side capsules on main stem and branch capsules were lighter than central ones of main stem, and upper capsules of four carpels eight loculi type decreased more seriously. BTB type demonstrated relatively better growth compared to the growth of BTQ type in one thousand grain weight. The maximum grain filling duration for germination percentage increased rapidly up to 40th day after flowering. Above 70% germinability was obtained from 40th day after flowering. Harvesting time of physiological maturity was considered to be 45th day after flowering with peaks of 2.14g of one thousand grain weight, 26% of grain water content and 90% of germinability.

• Journal of the Korean Magnetics Society
• /
• v.4 no.2
• /
• pp.122-125
• /
• 1994

The magnetic properties of Nd-Fe-B alloys of containing 4 at.% Nd have been studied for the development of new type rare-earth magnets. The amorphous phase of a melt-spun $Nd_{4}Fe_{85.5}B_{10.5}$ alloy is transformed into the phases which have a small amount of $Nd_{2}Fe_{14}B_{1}$ in ${\alpha}-Fe$ matrix by annealing above their crystallization temperature. The addition of Mo, Nb, V or Cu to $Nd_{4}Fe_{85.5}B_{10.5}$ alloy results in the reduction of grain size and the sub¬sequent improvement of the coercivity. The coercivity of $Nd_{4}Fe_{82}B_{10}M_{3}Cu_{1}$(M = Mo, Nb, V) alloys increases in the order of M = V < Nb < Mo and shows the highest value of 2.7 kOe when M = Mo. On the other hand, the rem¬anence of these alloys shows the opposite trend and the rn>st improved value of 1.35 T is observed when M = V.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.10
• /
• pp.646-650
• /
• 2017

We have evaluated the ferroelectric and electrical properties of pure $BiFeO_3$ (BFO) and $Bi_{0.9}A_{0.1}Fe_{0.975}V_{0.025}O_{3+{\alpha}}$ (A=Nd, Tb) thin films on $Pt(111)/Ti/SiO_2/Si(100)$ substrates by using a chemical solution deposition method. The remnant polarization ($2P_r$) of the $Bi_{0.9}Tb_{0.1}Fe_{0.975}V_{0.025}O_{3+{\alpha}}$ (BTFVO) thin film was approximately $65{\mu}C/cm^2$, with a maximum applied electric field of 950 kV/cm and a frequency of 10 kHz, where as that of the $Bi_{0.9}Nd_{0.1}Fe_{0.975}V_{0.025}O_{3+{\alpha}}$ (BNFVO) thin film was approximately $37{\mu}C/cm^2$ with a maximum applied electric field of 910 kV/cm. The leakage current density of the co-doped BNFVO thin film was four orders of magnitude lower than that of the pure BFO thin film, at $2.75{\times}10^{-7}A/cm^2$ with an applied electric field of 100 kV/cm. The grain size and uniformity of the co-doped BNFVO and BTFVO thin films were improved, in comparison to the pure BFO thin film, through structural modificationsdue to the co-doping with Nd and Tb.

• Transactions on Electrical and Electronic Materials
• /
• v.10 no.3
• /
• pp.80-84
• /
• 2009

The microstructure, voltage-current, capacitance-voltage, and dielectric characteristics of CCT doped Zn/Pr-based varistors were investigated at different sintering temperatures. As the sintering temperature increased, the average grain size increased from 4.3 to 5.1 ${\mu}m$ and the sintered density was saturated at 5.81 g $cm^{-3}$. As the sintering temperature increased, the breakdown field decreased from 7,532 to 5,882 V $cm^{-1}$ and the nonlinear coefficient decreased from 46 to 34. As the sintering temperature increased, the donor density, density of interface states, and barrier height decreased in the range of (9.06-7.24)${\times}10^{17}\;cm^{-3}$, (3.05-2.56)${\times}10^{12}\;cm^{-2}$, and 1.1-0.95 eV, respectively. The dielectric constant exhibited relatively low value in the range of 529.1-610.3, whereas the $tan{\delta}$ exhibited a high value in the range of 0.0910-0.1053.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.5
• /
• pp.313-319
• /
• 2018

This study introduces a new investigation report on the microstructural and electrical property changes of $ZnO-Zn_2BiVO_6-Mn_3O_4$ (ZZMn), where 0.33 mol% of $Mn_3O_4$ and 0.5 mol% of $Zn_2BiVO_6$ were added to ZnO (99.17 mol%) as liquid phase sintering aids. $Zn_2BiVO_6$ contributes to the decrease of sintering temperatures by up to $800^{\circ}C$, and segregates its particles at the grain boundary, while $Mn_3O_4$ enhances ${\alpha}$, the nonlinear coefficient, of varistor properties up to ${\alpha}=62$. In comparison, when the sintering temperature is increased from $800^{\circ}C$ to $1,000^{\circ}C$, the resistivity of ZnO grains decreases from $0.34{\Omega}cm$ to $0.16{\Omega}cm$, and the varistor property degrades. Oxygen vacancy ($V_o^{\bullet}$) (P1, 0.33~0.36 eV) is formed as a dominant defect. Two different kinds of grain boundary activation energies of P2 (0.51~0.70 eV) and P3 (0.70~0.93 eV) are formed according to different sintering temperatures, which are tentatively attributed to be $ZnO/Zn_2BiVO_6$-rich interface and ZnO/ZnO interface, respectively. Accordingly, this study introduces a progressive method of manufacturing ZnO chip varistors by way of sintering ZZMn-based varistor under $900^{\circ}C$. However, to procure a higher reliability, an in-depth study on the multi-component varistors with double-layer grain boundaries should be executed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.178-178
• /
• 2008

ZnO 바리스터는 인가되는 전압에 따라 저항이 변하는 전압 의존형 저항체이며 각종 전기 전자 정보통신용 제품에 정전기(ESD) 대책용 소자로 폭 넓게 사용되는 전자 세라믹스 부품이다. 특별히 Bi-based ZnO 바리스터는 다양한 상(phase)으로 구성되어 있으며 그 입계의 전기적 특성은 소량 첨가되는 dopant의 종류에 따라 다양하게 변하는 것으로 알려져 있다. 본 연구에서는 Bi-based ZnO 바리스터 (ZnO-$Bi_2O_3$, ZnO-$Bi_2O_3-Mn_3O_4$)에서 각종 유전함수$(Z^*,M^*,\varepsilon^*,Y^*,tan{\delta})$를 이용하여 입계의 주파수-온도에 대한 특성을 살펴 보았다. 일반적인 ZnO 바리스터 제조법으로 시편을 제작하여 78K~800K 온도 범위에서 각종 유전함수를 이용하여 복소 평면도(complex plane plot)와 주파수 응답도(frequency explicit plot)의 방법으로 defect level과 입계 특성(활성화 에너지, 정전용량, 저항, 입계 안정성 등)에 대하여 고찰하였다. ZnO-$Bi_2O_3$(ZB)계와 ZnO-$Bi_2O_3-Mn_3O_4$(ZBM)계 모두 상온 이하의 온도에서 $Zn_i$와 $V_o$의 결함이 나타났으며, 이들의 결함 준위는 각 유전함수에 따라 다소 차이가 났다. 입계 특성으로 ZB계는 이상구간(560~660K)을 전후로 1.15 eV $\rightarrow$ 1.49 eV의 활성화 에너지의 변화가 나타났지만, ZBM계는 이러한 현상이 나타나지 않았다. 또한 입계 전위 장벽의 온도 안정성에 대해서는 Cole-Cole model을 적용하여 분포 파라미터 (distribution parameter; $\alpha$)를 구하여 고찰하였다. ZB계의 입계 안정성은 온도에 따라 불안정해 졌지만, ZBM계는 안정하였다.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.46 no.8
• /
• pp.61-70
• /
• 2009

A 10b 30MS/s pipelined ADC operating under 1V power supply is presented. It utilizes a switched-RC based input sampling circuit and a resistive loop to reset the feedback capacitor in the multiplying digital-to-analog converter (MDAC) for the low-voltage operation. Cascaded switched-RC branches are used to achieve accurate grain of the MDAC for the first stage and separate switched-RC circuits are used in the sub-ADC to suppress the switching noise coupling to the MDAC input The measured differential and integral non-linearities of the prototype ADC fabricated in a 0.13${\mu}m$, CMOS process are less than 0.54LSB and 1.75LSB, respectively. The prototype ADC achieves 54.1dB SNDR and 70.4dB SFDR with 1V supply and 30MHz sampling frequency while consuming 17mW power.

• Korean Journal of Materials Research
• /
• v.22 no.8
• /
• pp.385-389
• /
• 2012

Significant improvements in the switching voltage distribution are required for the development of unipolar resistive memory devices using $MnO_x$ thin films. The $V_{set}$ of the as-grown $MnO_x$ film ranged from 1 to 6.2 V, whereas the $V_{set}$ of the oxygen-annealed film ranged from 2.3 to 3 V. An excess of oxygen in an $MnO_x$ film leads to an increase in $Mn^{4+}$ content at the $MnO_x$ film surface with a subsequent change in the $Mn^{4+}/Mn^{3+}$ ratio at the surface. This was attributed to the change in $Mn^{4+}/Mn^{3+}$ ratios at the $MnO_x$ surface and to grain growth. Oxygen annealing is a possible solution for improving the switching voltage distribution of $MnO_x$ thin films. In addition, crystalline $MnO_x$ can help stabilize the $V_{set}$ and $V_{reset}$ distribution in memory switching in a Ti/$MnO_x$/Pt structure. The improved uniformity was attributed not only to the change of the crystallinity but also to the redox reaction at the interface between Ti and $MnO_x$.

• Journal of the Korean Ceramic Society
• /
• v.20 no.3
• /
• pp.193-198
• /
• 1983

This experiment has been carried out for the purpose of investigating the effect of $V_2O_5$ and $H_3BO_3$ additives on sintering of magnesium oxide over the temperature range of 1300-150$0^{\circ}C$ MgO powder has been obtained by calcin-ing extra reagent grade magnesium carbonate(basic) at 90$0^{\circ}C$ for 30 minutes. The specimens were prepared by compression with pressure of 700Kg/cm2 then fired at 1300-150$0^{\circ}C$ for 0-5hrs. Sintering behaviour and microstructure of fired specimens were examined. Densification rates obeyed the equation D=K 1n t+C. The ratio of density in case of addition of $V_2O_5$ to theoretical density of pure periclase was 95-99% Activation energy of densification in case of $V_2O_5$ addition was 30.15 Kcal/mole. The range of average grain size in case of addition of $V_2O_5$ was 40-50$\mu\textrm{m}$. $H_3BO_3$ addtivie had not an effect on densification of MgO.