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Silver-Tantalate-Niobate Thick Film의 유전 특성 연구
이규탁,윤석우,강이구,고중혁,Lee, Ku-Tak,Yun, Seok-Woo,Kang, Ey-Goo,Koh, Jung-Hyuk 한국전기전자재료학회 2010 전기전자재료학회논문지 Vol.23 No.7
Low loss perovskite niobates and tantalates have been placed on a short list of functional materials for future technologies. In this study, we fabricated Ag(Ta,Nb)$O_3$ thick films on the $Al_2O_3$ substrates by the screen printing method. The Ag(Ta,Nb)$O_3$ powders were fabricated by the mixed oxide method. The sintering temperature and time were $1150^{\circ}C$ and 2 hrs, respectively. The results of XRD analysis showed that the specimens employed in this study had the pesudo cubic structure. The dielectric permittivity and loss tangent of the films have been characterized from 1 kHz to 1 MHz. Also the dielectric permittivity and loss tangent were measured from 303 K to 393 K. The electrical properties of the film are also discussed.
이규탁,박정수,윤지선,조정호,정영훈,백종후,Lee, Ku Tak,Park, Jung Soo,Yun, Ji Sun,Cho, Jeong Ho,Jeong, Young Hun,Paik, Jong Hoo 한국전기전자재료학회 2014 전기전자재료학회논문지 Vol.27 No.11
The $0.99Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3-0.01LaAlO_3$, $0.01LaMnO_3$ or $0.01LaFeO_3$ (0.99BNKT-0.01LA, 0.01LM or 0.01LF) ceramics were prepared by a conventional mixed mothod. The structure and morphology of the lead free ceramics were characterized by XRD (X-ray diffraction) and FE-SEM (field emission scanning electron microscopy). XRD results indicated that the BNKT ceramics modified by LA, LM or LF induced a transition from a ferroelectric tetragonal to a non-polar pseudo-cubic phase, leading to decrease in the remnant polarization ($P_r$) and coercive field ($E_c$) in the P-E hysterisis loops. The effects of the BNKT ceramics modified by La-based $ABO_3$ pervskite structure on the electric-field induced strain were investigated, and the largest normalized unipolar strain ($S_{max}/E_{max}$) was found in BNKT-0.01LF ceramic.
Glass Substrate와 PET Film위에 Screen Printing된 ZnO Thick Film의 구조적 전기적 특성
이규탁,전민철,채문순,이경주,문병무,고중혁,Lee, Ku-Tak,Jeon, Min-Cheol,Chae, Moon-Soon,Lee, Kyung-Ju,Moon, Byung-Moo,Koh, Jung-Hyuk 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.5
As a II-IV compound semiconductor, ZnO has a wide band gap of 3.37 eV with transparent properties. Due to this transparent properties, ZnO materials can be also employed as the transparent conducting electrode materials. Recently, rapid progress has been made in the field of DSSC (dye sensitized solar cell)area. Therefore, strong demands have been required for the transparent electrodes with low temperature processing and cheap cost. In this paper, we will prepare ZnO thick films on the PET substrates for the electrode applications. We will investigate the structural and microstructure properties through the XRD, and SEM analysis, respectively. Also, we will study the electrical of specimens to apply the conducting electrode.
BaTiO₃ 기반의 적층 세라믹 캐피시터 (Multi-Layer Ceramic Capacitors)의 절연저항 열화 메커니즘과 신뢰성 분석 동향
이규탁(Ku-Tak Lee),천진성(Jinsung Chun),조욱(Wook Jo) 한국세라믹학회 2023 세라미스트 Vol.26 No.2
The demand for high performance multilayer ceramic capacitors (MLCCs) has rapidly increased keeping up with the recent trends in electronics seeking better performance per volume. It follows that thinning of dielectric layers of MLCC and atomization of powders have become two most challenging issues these days. However, it is well known that these two approaches are not free from reliability issues. In this brief review, we introduce the commonly accepted models that explain how dielectric materials fail during operation and how to evaluate the lifetime of MLCCs with a real world example.
이동현,이승환,이성갑,이규탁,이영희,Lee, Dong-Hyun,Lee, Seung-Hwan,Lee, Sung-Gap,Lee, Ku-Tak,Lee, Young-Hie 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.7
We studied sintering temperature to enhance the piezoelectric properties of $0.98(Na_{0.5}K_{0.5})NbO_3-0.02Li(Sb_{0.17}Ta_{0.83})O_3$+0.01wt%ZnO (hereafter NKN-LST+ZnO) lead free piezoelectric ceramics. The synthesis and sintering method were the conventional solid state reaction method and sintering was executed at $1,080\sim1,120^{\circ}C$. We found that NKN-LST+ZnO ceramics at optimal sintering temperature showed the improved piezoelectric properties at the optimal sintering temperature. The NKN-LST+ZnO ceramics show good performance with piezoelectric constant $d_{33}$= 153 pC/N sintered at $1,090^{\circ}C$. The results reveal that NKN-LST+ZnO ceramics are promising candidate materials for lead-free piezoelectric application.
박정수,이규탁,윤지선,조정호,정영훈,백종후,Park, Jung Soo,Lee, Ku Tak,Yun, Ji Sun,Cho, Jeong Ho,Jeong, Young Hun,Paik, Jong Hoo 한국전기전자재료학회 2014 전기전자재료학회논문지 Vol.27 No.12
$Bi_{0.5+x}(Na_{0.78}K_{0.22})_{0.5-3x}TiO_3$ ceramics with an excess $Bi^{3+}$ and a deficiency of $Na^+$ and $K^+$ were synthesized by a conventional solid state reaction method. The structure and morphology of $Bi_{0.5+x}(Na_{0.78}K_{0.22})_{0.5-3x}TiO_3$ ceramics were characterized by X-ray diffraction and field emission scanning electron microscopy. The electric polarization and mechanical strain induced by external electric field, and the temperature dependence of dielectric constant were investigated. These results demonstrated that an ergodic relaxor phase can be induced by controls of the mole ratio of $Bi^{3+}$, $Na^+$ and $K^+$. A phase boundary between non-ergodic and ergodic relaxor phases can be observed at ambient temperature. The ergodic relaxor phase can be transferred to the ferroelectric phase by application of the electric field. The stability of the induced ferroelectric phases strongly depends on the mole ratio of $Bi^{3+}$, $Na^+$ and $K^+$. The maximum strain of 0.31% was observed in $Bi_{0.51}(Na_{0.78}K_{0.22})_{0.47}TiO_3$ ceramics sintered at $1,150^{\circ}C$ for 2 h.
Spin-coating을 이용하여 Flexible Film에 제작된 ZnO TCO의 특성 분석
전민철,이규탁,박상욱,이경주,문병무,조원주,고중혁,Jun, Min-Chul,Lee, Ku-Tak,Park, Sang-Uk,Lee, Kyung-Ju,Moon, Byung-Moo,Cho, Won-Ju,Koh, Jung-Hyuk 한국전기전자재료학회 2012 전기전자재료학회논문지 Vol.25 No.4
This article introduces the characterization of spin coated ZnO transparent conducting oxide on the flexible substrates. As a II-IV compound semiconductor, ZnO has a wide band gap of 3.37 eV with transparent properties. Due to this transparent properties, ZnO materials can be also employed as the transparent conducting electrode materials. Therefore, strong demands have been required for the transparent electrodes with low temperature processing and cheap cost. So, We will investigate the electrical property and optical transmittance of ZnO transparent conducting oxide through the 4-point probe resistivity meter, and ultraviolet-vis spectrometer Lamda 35, respectively.
박정수,이규탁,조정호,정영훈,백종후,윤지선,Park, Jung Soo,Lee, Ku Tak,Cho, Jeong Ho,Jeong, Young Hun,Paik, Jong Hoo,Yun, Ji Sun 한국세라믹학회 2014 한국세라믹학회지 Vol.51 No.6
$0.97Bi_{0.5+x}(Na_{0.78}K_{0.22})_{0.5-3x}TiO_3-0.03LaFeO_3$ lead-free piezoelectric ceramics were fabricated by a solid state reaction method. $LaFeO_3$ additives were added to $Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3$ for volatile compensation of bismuth and sodium ions in the sintering process. To create A-site vacancies, the mole ratio and charge valence of A-site ions ($Bi^{3+}$, $Na^+$ and $K^+$) were controlled. The improved piezoelectric properties were observed by addition of $LaFeO_3$ and control of A-site vacancies. In particular, a $d_{33}^*(S_{max}/E_{max})$ value of 614pm/V and an electric field induced strain of 0.33% was observed in $0.97Bi_{0.505}(Na_{0.78}K_{0.22})_{0.485}TiO_3-0.03LaFeO_3$ ceramic.
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.