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Li Dopant가 ZnO 세라믹스의 전기적 특성과 미세 구조에 미치는 영향
전민철,고중혁,Jun, Min-Chul,Koh, Jung-Hyuk 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.4
It is well known that Zinc Oxide (ZnO) is an attractive material for its various applications. ZnO has been mostly used as a transparent conducting oxide in liquid crystal displays, solar cells due to its advantages of low cost, high productivity, and excellent electrical conductivity. Notably, flexible-dye-sensitized solar cells (DSSCs) based on polyethylene terephthalate (PET) substrates require low temperature sintering processing conditions. Therefore, low temperature processing conditions have been strongly required for transparent conducting film applications. In this paper, we prepared low temperature-sintered ZnO ceramics employing Li as a sintering aid.
강우석,고중혁,Kang, Woo-Seok,Koh, Jung-Hyuk 한국전기전자재료학회 2014 전기전자재료학회논문지 Vol.27 No.12
Energy problem has been issued in worldwide because fossil fuel has being almost exhausted. A lot of renewable energy have been received attention to replace the energy from fossil fuel. Among them, piezoelectric energy harvester is one of excellent candidates. In general, micro scaled small sized energy harvesters were usually based on the lithography process. However, these lithography process require complicated process and high cost. In this paper, a new process has been proposed for micro-scaled piezoelectric energy harvester. $0.2Pb(Mg_{1/3}Nb_{2/3})O_3-0.8Pb(Zr_{0.52}Ti_{0.48})O_3$ composition was used as piezoelectric material due to excellent piezoelectric properties and also can be easily prepared by mixed oxide method.
에어로졸 데포지션 법을 이용하여 제조한 SiO<sub>2</sub> 후막의 구조 및 광학 특성
장찬익,고중혁,Jang, Chan-Ik,Koh, Jung-Hyuk 한국전기전자재료학회 2013 전기전자재료학회논문지 Vol.26 No.1
Aerosol deposition(AD) coating that enable fabricate films at low temperature have begun to be widely researched for the integration of ceramics as well to realize high-speed deposition rates. For application of ceramic thick film by AD to display and electronic ceramic industry, fabrication of dense structure with a no cracking is required. In this study, to fabricate dense ceramic thick film, the effect of crystal phase of starting powder was investigated. For this study, amorphous and crystalline $SiO_2$ powders were used as starting powders. Two types of $SiO_2$ powders were deposited on glass substrate by AD. In the case of amorphous $SiO_2$ powder, the deposited films had extremely incompact and opaque layer, irrespective of particle size. In contrast to amorphous powder, in the case of crystalline powder, porous structure layer and dense microstructure with no cracking layer were fabricated depending on the particle size. The optimized starting powder size for dense coating layer was $1{\sim}2{\mu}m$. The transmittance of film reached a maximum of 76% at 800 nm.
스크린 프린팅 기법으로 제작된 ZnBO 첨가 (Ba,Sr)TiO<sub>3</sub> Planner Capacitor 특성 분석
문상호,고중혁,Moon, Sang-Ho,Koh, Jung-Hyuk 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.9
We have fabricated (Ba,Sr)TiO3$TiO_3$ thick films doped with various amount of ZnBO dopants (1, 3, and 5 wt%) by screen printing method on the alumina substrates, which were sintered at the temperature below $1200^{\circ}C$. With increasing the amount of ZnBO dopants, the relative dielectric permittivity of ZnBO doped (Ba,Sr)$TiO_3$ was decreased, while loss tangent was increased. 1 wt% ZnBO doped (Ba,Sr)$TiO_3$ thick film has relative dielectric permittivity of 759 at 1 MHz, while 3 and 5 wt% of ZnBO doped (Ba,Sr)$TiO_3$ thick films have 624 and 554, respectively. By introducing ZnBO dopants to the (Ba,Sr)$TiO_3$ thick films, leakage current densities were decreased. The decreased leakage current with increasing ZnBO dopants can be explained by increased density and grain size of thick film on alumina substrate. We believe this decreased leakage current density probably come from the increased grain size and increased density.
채문순,이규탁,고중혁,Chae, Moon-Soon,Lee, Ku-Tak,Koh, Jung-Hyuk 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.10
1 mol% $Li_2O$ excess $0.9(Na_{0.52}K_{0.48})NbO_3-0.1LiTaO_3$ lead-free piezoelectric multilayer ceramic actuators were investigated to determine their aging properties. To reduce the thermal aging behavior, we applied a rectified unipolar electric field of 5 kV/mm to the specimen to accelerate the electric aging behavior. By employing a rectified unipolar electric field for the piezoelectric actuators, we could remove undesirable heating from the relaxation current in the motion of the ferroelectric domain. To accelerate the aging test, the applied electric fields had a frequency of 900 Hz. To have enough time for charging and discharging, we employed an accurate time constant to design the equivalent circuit model for the aging tester. To extract exact aging behavior, we measured the pseudo-piezoelectric coefficient before and after the aging process. We also measured the electro-mechanical coupling coefficient, the frequency-dependent dielectric permittivity, and the impedance to compare with fresh and aged specimen.
이경수,신동진,고중혁,Lee, Kyoung-Soo,Shin, Dong-Jin,Koh, Jung-Hyuk 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.4
In this paper, we have proposed piezoelectric energy harvester employing the pillar structure with the diameter size of 500 um. So we have selected the Su-8 photo-resist and modified lithography process to manufacture the pillar structure with height above the $500{\mu}m$. Simultaneously, we tried to make a comparative study to use ceramic bulk - polymer structure In this paper, we will report the process and properties of micro pillar structure based on the PMN-PZT ($Pb(Mg_{1/3}Nb_{2/3})O_3-PbZrTiO_3$) materials. Finally, We will propose a method for generating electrical energy with a piezoelectric element using vibration, an energy source can be obtained from the "clean" energy.
MgO가 첨가된 $Ba_{0.5}Sr_{0.5}TiO_3$ 후막의 구조 및 유전 특성
강원석,남성필,고중혁,이성갑,이영희,Kang, Won-Seok,Nam, Sung-Pil,Koh, Jung-Hyuk,Lee, Sung-Gap,Lee, Young-Hie 대한전기학회 2006 전기학회논문지C Vol.55 No.12
Using the $Ba_{0.5}Sr_{0.5}TiO_3$(BST) powders prepared by the Sol-Gel method, the BST thick films were fabricated on the $Al_2O_3 $substrates coated with Pt by the screen printing method. Compared with pure BST thick films, the structural and dielectric properties of the BST thick films doped with $1{\sim}10$ wt % MgO were investigated. It was observed that the Mg substitution into BST causes a shift in the cubic-tetragonal BST phase transition peak to a lower temperature. The microstructure of the BST substituted with Mg was homogeneous and dense. Mg substitution into BST had a significant effect on the grain size reduction. Dielectric constant was decreased with increasing the MgO content and temperature. In the case of BST thick films doped with 1 wt% MgO, the relative permittivity and dielectric loss were 1581 and 1.4 % at 1 MHz.
Ag<sub>2</sub>O 첨가량에 따른 0.95(Na,K)NbO<sub>3</sub>-0.05LiNbO<sub>3</sub> 세라믹스의 압전 특성
채문순,신동진,고중혁,Chae, Moon-Soon,Shin, Dong-Jin,Koh, Jung-Hyuk 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.6
As lead-free piezoelectric materials, $Ag_2O$ doped $0.95(K_{0.5}Na_{0.5})NbO_3-0.05LiNbO_3+x$ mol% (where x = 0, 0.5, 1, 1.5, 2, 2.5 and 3, respectively) ceramics were fabricated by a conventional sintering process. The doping effects on the microstructure and electrical properties of the $0.95(K_{0.5}Na_{0.5})NbO_3-0.05LiNbO_3$ ceramics were systematically investigated. When the 3 mol % $Ag_2O$ doped $0.95(K_{0.5}Na_{0.5})NbO_3-0.05LiNbO_3$ samples were sintered at $1,080^{\circ}C$ for 5 hrs in air, these ceramics showed excellent values of density=4.20 $g/cm^3$, piezoelectric constant ($d_{33}$)=174 pC/N and phase transition temperature$(T_c)=421.6^{\circ}C$, respectively.