ZnO 세라믹스 거대입성장

김영정,Kim, Young Jung 한국결정성장학회 2019 韓國結晶成長學會誌 Vol.29 No.6

In the process of ZnO ceramic sintering at a temperature of 1385℃, higher than the normal sintering temperature, some grains were growth up to mm scale. When sintered at 1400℃ for 8 hours, the size of the grains that are not involved in the abnormal growth is as large as 30~40 ㎛, but the size of the abnormal grown grain reaches 1,000 ㎛, which is more than 10,000 times bigger in volume than the normal one within 8 hr growth. As a cause of rapid and abnormal grain growth, primary particle size distribution, compaction density variation within sample and doping of impurities could be considered. The primary particle size distribution could be considered main reason for abnormal grain growth but no solid evidence was obtained. Through the observation of the microstructure, it is presumed that the giant grains grow absorbing the neighbor grains through a grain rotation process. ZnO를 통상적인 소결온도 이상의 온도 1385℃에서 소결하는 과정에서 mm 크기로 거대 성장된 입자를 갖는 세라믹스를 제조하였다. 1400℃에서 8시간 소결하는 경우 성장에 참여하지 않은 입자의 크기는 30~40 ㎛이고 거대 성장된 입자는 1,000 ㎛에 달하여 부피비 최소 10,000배 이상의 급속한 성장이 이루어졌다. 이러한 급속한 성장의 원인으로 일차 입자 크기분포, 성형압 불균일 또는 불순물의 합입등을 고려하였으며, 이들 중 일차입자 크기 분포일 것으로 추정되나 확실한 증거를 확보하지 못하였다. 미세구조 관찰을 통해 거대입자 성장은 주변의 입자를 통째로 합치는 과정을 통해 성장하는 것으로 추정된다.

Atomic Arrangements of Asymmetrically-tilted Grain Boundaries in 30˚ Rotation Domains of ZnO Thin Films Grown on n-Si Substrates

J. M. Yuk,Y. S. No,J. Y. Kim,W. K. Choi,김태환 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.1

Selected-area electron diffraction patterns for ZnO/Si heterostructures annealed at 800℃ showed that 30˚ rotation domains were generated in the ZnO thin films. The plane-view high-resolution transmission electron microscopy (HRTEM) images for the ZnO thin films grown on n-Si substrates annealed at 800℃ showed that asymmetrical tilt grain boundaries were tilted by 16.5˚ and 13.5˚ from two grains with a 30˚ tilted angle. The grain boundary planes of the two grains were (3580) and (2350). The atomic arrangements of the asymmetrically-tilted grain boundaries in 30˚ rotation domains of ZnO thin films grown on n-Si substrates annealed at 800℃ are described on the basis of the HRTEM results.

Mn₃O₄ 함량에 따른 ZnO의 결함과 입계 특성

홍연우,신효순,여동훈,김진호,Hong, Youn-Woo,Shin, Hyo-Soon,Yeo, Dong-Hun,Kim, Jin-Ho 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.12

In this study, we investigated the effects of Mn dopant (0.1~3.0 at% $Mn_3O_4$ sintered at 1000$^{\circ}C$ for 1 h in air) on the bulk trap (i.e. defect) and grain boundary properties of ZnO, ZM(0.1~3.0) using admittance spectroscopy (AS), and impedance-modulus spectroscopy (IS & MS). As a result, three kinds of defect were found below the conduction band edge of ZnO as 0.09~0.14 eV (attractive coulombic center), 0.22~25 eV ($Zn^{{\cdot}{\cdot}}_i$), and 0.32~0.33 eV ($V^{\cdot}_o$). The oxygen vacancy increased with Mn doping. In ZM, an electrically single grain boundary as double Schottky barrier was formed with 0.82~1.0 eV of activation energies by IS & MS. We also find out that the barriers of grain boundary of Mn-doped ZnO (${\alpha}$-factor=0.13) were more stabilized and homogenized with temperature compared to pure ZnO.

ZnO-Zn₂BiVO₆-Co₃O₄-Cr₂O₃-CaCO₃ 바리스터 내의 결정결함과 입계특성

홍연우,하만진,Hong, Youn-Woo,Ha, Man-Jin 한국전기전자재료학회 2019 전기전자재료학회논문지 Vol.32 No.4

In this study, we investigated the crystal defects and grain boundary properties in a ZZCCC ($ZnO-Zn_2BiVO_6-Co_3O_4-Cr_2O_3-CaCO_3$) varistor, with the liquid-phase sintering aid $Zn_2BiVO_6$ developed by our laboratory. The ZZCCC varistor sintered at $1,200^{\circ}C$ exhibited excellent nonlinear current-voltage characteristics (${\alpha}=63$), with oxygen vacancy ($V_o^*$ ; 0.35 eV) as a main defect, and an apparent activation energy of 1.1 eV with an electrically single grain boundary. Therefore, among the various additives to improve the electrical properties of ZnO varistors, if $Zn_2BiVO_6$ is used as a liquid phase sintering aid, it will be ideal to use Co for the oxygen vacancy and Ca for the electrically single grain boundary. This will allow the good properties of ZnO varistors to be maintained up to high sintering temperatures.

Cr을 첨가한 ZnO의 결함과 입계 특성

홍연우,신효순,여동훈,김종희,김진호,Hong, Youn-Woo,Shin, Hyo-Soon,Yeo, Dong-Hun,Kim, Jong-Hee,Kim, Jin-Ho 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.11

In this study, we investigated the effects of Cr dopant (1.0 at% $Cr_2O_3$ sintered at $1000^{\circ}C$ for 1 h in air) on the bulk trap (i.e. defect) and interface state levels of ZnO using dielectric functions ($Z^*$, $M^*$, $Y^*$, $\varepsilon^*$, and $tan{\delta}$), admittance spectroscopy (AS), and impedance-modulus spectroscopy (IS & MS). For the identification of the bulk trap levels, we examine the zero-biased admittance spectroscopy and dielectric functions as a function of frequency and temperature. Impedance and electric modulus spectroscopy is a powerful technique to characterize grain boundaries of electronic ceramic materials as well. As a result, three kinds of bulk defect trap levels were found below the conduction band edge of ZnO in 1.0 at% Cr-doped ZnO (Cr-ZnO) as 0.11 eV, 0.21 eV, and 0.31 eV. The overlapped defect levels ($Zn^{..}_i$ and $V^{\cdot}_0$) in admittance spectra were successfully separated by the combination of dielectric function such as $M^*$, $\varepsilon^*$, and $tan{\delta}$. In Cr-ZnO, the interfacial state level was about 1.17 eV by IS and MS. Also we measured the resistance ($R_{gb}$) and capacitance ($C_{gb}$) of grain boundaries with temperature using impedance-modulus spectroscopy. It have discussed about the stability and homogeneity of grain boundaries using distribution parameter ($\alpha$) simulated with the Z"-logf plots with temperature.

전자빔 표면조사에 따른 ZnO/Ag/ZnO 박막의 전기광학적 완성도 연구

김현진(Hyun-Jin Kim),이연학(Yeon-Hak Lee),장진규(Jin-Kyu Jang),최재욱(Jae-Wook Choi),최수현(Su-Hyeon Choe),허성보(Sung-Bo Heo),김준호(Jun-Ho Kima),김대일(Daeil Kim) 한국생산제조학회 2023 한국생산제조학회지 Vol.32 No.1

Transparent ZnO/Ag/ZnO tri-layered films were deposited on a glass substrate using radio frequency and direct current magnetron sputtering. The thicknesses of the ZnO and Ag films were maintained at 30 and 10 nm, respectively, to consider the effects of electron irradiation on the optoelectrical properties of the films. XRD spectra revealed that post-deposition electron irradiated films exhibited characteristic peaks of ZnO (002) and Ag (111), respectively. The observed grain sizes of ZnO (002) and Ag (111) increased to 7.1 and 8.4 nm, respectively, under an irradiation condition of 900 eV, and the surface roughness of the electron irradiated films at 900 eV was reduced to 1.29 nm. The as-deposited films showed a figure of merit, indicating the optoelectrical performance of the films, of 4.1×10<SUP>-3</SUP> Ω<SUP>-1</SUP>, whereas the films electron irradiated at 900 eV showed a higher figure of merit of 1.1×10<SUP>-2</SUP> Ω<SUP>-1</SUP>.

ZnO 산화물의 열적 전기적 특성

박보석,홍광준,신동찬,이우선,김호기,박진성 한국세라믹학회 2003 한국세라믹학회지 Vol.40 No.5

ZnO 미세 분말을 sol-gel법으로 제조하였다. Gel분말의 형상은 하소 열 처리 온도에 따라 판상, 침상,그리고 구형으로 변화하였고, $700^{\circ}C$ 이하 하소 온도에서는 온도에 따른 입자 성장 속도가 낮았지만, $700^{\circ}C$ 이상의 온도부터 급격한 입자 성장 속도를 나타내었다. 입자 사이즈가 커질수록 결정화 정도는 더 커졌고, gel분말의 유기 화합물들은 30$0^{\circ}C$ 이하 온도에서 휘발되었다. 열 처리 온도에 따른 ZnO 분말은 S자형(sigmoidal shape)의 전기전도성 거동을 보였고, gel분말의 열처리 온도가 감소할수록 일정한 전도성이 일정한 온도 구간이 좁게(narrow) 나타났다. 최적의 CO 기체 센싱 특성은 50$0^{\circ}C$의 하소 열처리한 시편에서 나타났고, 열처리 온도가 올라갈수록 센싱 특성은 감소하였다. Fine powders of ZnO were synthesized by the sol-gel method. The shape of gel powders with calcination temperatures changed into the sheet structure, the needle shape, and the spherical grain. The growth rate of grain size was slow to 700$^{\circ}C$ but high above 700$^{\circ}C$. The bigger the grain size is, the higher the degree of crystallization is. The organic element in gel powders evaporated below 300$^{\circ}C$. Temperature dependence of conductances showed the sigmoidal shape, but the temperature range of the constant conductances narrowed with the decrement of the calcination temperature of gel powders. The optimum sensing property for CO gas were observed with the specimen calcined at 500$^{\circ}C$ and degraded with the increment of calcination temperature.

ZnO-Bi₂O₃-Mn₃O₄-Co₃O₄ 바리스터의 결함과 전기적 특성

홍연우,이영진,김세기,김진호,Hong, Youn-Woo,Lee, Young-Jin,Kim, Sei-Ki,Kim, Jin-Ho 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.12

In this study, we have investigated the effects of Mn and Co co-doping on defects, J-E curves and grain boundary characteristics of ZnO-$Bi_2O_3$ (ZB) varistor. Admittance spectra and dielectric functions show two bulk defects of $Zn_i^{{\cdot}{\cdot}}$ (0.17~0.18 eV) and $V_o^{\cdot}$ (0.30~0.33 eV). From J-E characteristics the nonlinear coefficient (${\alpha}$) and resistivity (${\rho}_{gb}$) of pre-breakdown region decreased as 30 to 24 and 5.1 to 0.08 $G{\Omega}cm$ with sintering temperature, respectively. The double Schottky barrier of grain boundaries in ZB(MCo) ($ZnO-Bi_2O_3-Mn_3O_4-Co_3O_4$) could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.64 eV at lower temperature to 1.06 eV at higher temperature. It was revealed that a co-doping of Mn and Co in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against an ambient temperature (${\alpha}$-factor= 0.136).

소결온도가 ZnO-Co3O4-Cr2O3의 결함과 전기적 특성에 미치는 영향

홍연우 ( Youn Woo Hong ),김유비 ( You Bi Kim ),이영진 ( Young Jin Lee ),김세기 ( Sei Ki Kim ),백종우 ( Jong Hoo Paik ),조만호 ( Man Ho Jo ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.12

The defects and origin of the good varistor properties in the ZnO-Co3O4-Cr2O3 system were investigated by admittance spectroscopy, I-V characteristics, and impedance and modulus spectroscopy. Two kinds of defects were detected, but (0.27 eV) was identified as a major donor level by admittance spectroscopy. The ZnO grain resistivity of ~0.4 Ωcm was calculated but somewhat increased with sintering temperature. J-E characteristics with varistor behavior was seen in this system while the nonlinear coefficient α changed from 9 to 92 with sintering temperature. The single potential barrier of 0.64-1.01 eV at the grain boundary region was confirmed by impedance and modulus spectroscopy. The origin of a good varistor behavior in ZnO-Co3O4-Cr2O3 would be due to the formation and stabilization of a double Schottky barrier by the redox reaction of Co ions and the existence of small Cr ions in the grain boundaries.

ZnO-Bi₂O₃-Sb₂O₃ 세라믹스의 전기적 특성

홍연우,신효순,어동훈,김종희,김진호,Hong, Youn-Woo,Shin, Hyo-Soon,Yeo, Dong-Hun,Kim, Jong-Hee,Kim, Jin-Ho 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.8

In this study, it has been investigated on the changing behavior of electrical properties in $ZnO-Bi_2O_3-Sb_2O_3$ (Sb/Bi=2.0, 1.0 and 0.5) ceramics. The samples were prepared by conventional ceramic process, and then characterized by I-V, C-V curve plots, impedance and modulus spectroscopy (IS & MS) measurement. The electrical properties of ZBS systems were strongly dependent on Sb/Bi. In ZBS systems, the varistor characteristics were deteriorated noticeably with increasing Sb/Bi and the donor density and interface state density were increased with increasing Sb/Bi. On the other hand, we observed that the grain boundary reacted actively with the ambient oxygen according to Sb/Bi ratio. Especially the grain boundaries of Sb/Bi=0.5 systems were divided into two types, i.e. sensitive to oxygen and thus electrically active one and electrically inactive intergranular one with temperature. Besides, the increased pyrochlore and $\beta$-spinel phase with Sb/Bi ratio caused the distributional inhomogeneity in the grain boundary barrier height and the temperature instability. To the contrary, the grain boundary layer was relatively homogeneous and more stable to temperature change and kept the system highly nonlinear at high Bi-rich phase contents.