(Bi,La)FeO₃-PbTiO₃ 세라믹스의 자전효과

이은구,이종국,장우양,김선재,이재갑,Lee Eun Gu,Lee Jong Kook,Jang Woo Yang,Kim Sun Jae,Lee Jae Gab 한국재료학회 2005 한국재료학회지 Vol.15 No.2

Magnetoelectric (ME) effects for lanthanum modified $BiFeO_3-PbTiO_3\;(BE-_xPT)$ solid solutions have been investigated. The value of magnetoelectric polarization coefficient, up is 10 times greater than that of $Cr_2O_3$. The results also show that up is due to a linear coupling between polarization and magnetization, and that up is independent of do magnetic bias and ac magnetic field. The ME effect is believed to be significantly enhanced due to breaking of the cycloidal spin state of a long-period spiral spin structure, via randomly distributed charged imperfections.

$Pb(Zr,Ti)O_3$ 강유전체 박막 이력곡선의 변형에 관한 연구

이은구,이종국,이재갑,김선재,Lee, Eun-Gu,Lee, Jong-Guk,Lee, Jae-Gap,Kim, Seon-Jae 한국재료학회 2000 한국재료학회지 Vol.10 No.5

Deformation in the hysteresis loop of $Pb(Zr,Ti)O_3$ (PZT) thin films with various Zr/Ti ratios has been studied by varying the top electrode preparation method and the annealing temperature. Pt/PZT/Pt capacitors was found to be positively poled due to dc plasma potential generated during reactive ion etch (RIE) of Rt. Internal field is formed by space charges trapped at domain boundaries. Aging phenomenon such as constriction in the middle of the hysteresis loop was observed in the PZT film with top electrode deposited by sputtering. Top electrode annealing restores the hysteresis loop by removing the space charges. As Zr/Ti ratio decrease, voltage shift increases and an-nealing temperature at which internal field disappears also increases.

이종에피에 의해 증착한 BiFeO₃ 박막의 전기 및 자기특성

이은구,Lee Eun Gu,Viehland D. 한국재료학회 2004 한국재료학회지 Vol.14 No.10

$BiFeO_3$ films grown on (111) $SrTiO_3$ substrate have a rhombohedral structure, identical to that of single crystals. On the other hand, films grown on (110) or (001) $SrTiO_3$ substrate are monoclinically distorted from the rhombohedral structure due to the epitaxial constraint. The easy axis of spontaneous polarization is close to [111] for the variously oriented films. Dramatically enhanced polarization and magnetization have been found for hetero-epitaxially grown $BiFeO_3$ thin films comparing to that of $BiFeO_3$ crystals. The results are explained in terms of an epitaxially-induced transition between cycloidal and homogeneous spin states, via magneto-electric interactions.

수치해석을 이용한 전력 BJT의 정특성 분석

이은구,윤현민,김철성,Lee, Eun-Gu,Yun, Hyun-Min,Kim, Cheol-Seong 한국전기전자학회 2002 전기전자학회논문지 Vol.6 No.2

An algorithm for analyzing the characteristics of the power BJT using numerical analysis method is proposed. The Fermi-Dirac statistics is used to calculate the carrier concentration in highly doped region. Philips Unified mobility model, SRH model and Auger model is used to calculate the recombination current of base region. To verify the accuracy of the proposed method, the collector current of BANDIS is compared with the measured data in the condition of the base current increased from $1.0[{\mu}A]\;to\;3.5[{\mu}A]$. The collector current of BANDIS show a maximum relative error within 8.9% compared with the measured data.

습식 산화한 LPCVD Silicon Nitride층의 물리적, 전기적 특성

이은구,박진성,Lee, Eun-Gu,Park, Jin-Seong 한국재료학회 1994 한국재료학회지 Vol.4 No.6

The physical and electrical characteristics of sub-l0nm thick capacitor dielectrics formed by wet oxidation of silicon nitride(oxide/nitride composite) and by removing the top oxide of oxidized silicon nitride(0xynitride) are described. For the capacitors with an oxide/nitride composite layer, the capacitance decreases sharply, but the breakdown field increases with an increase in the wet oxidation time at $900^{\circ}C$. For the capacitors with oxynitride layers, the values of both the capacitance and the breakdown field increase with increasing wet oxidation time. The reduction of effective thickness and the improved quality of oxynitride film are responsible for the improved capacitance and increased breakdown fields, respectively. In addition, intrinsic TDDB characteristics and early breakdown failure rate of oxynitride film are improved with increasing oxidation time. Consequently, the oxynitride film is suitable for dynamic memories as a thin dielectric film.

<001> 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ 단결정의 상변화 및 유전 특성

이은구,이재갑,Lee, Eun-Gu,Lee, Jae-Gab 한국재료학회 2011 한국재료학회지 Vol.21 No.7

The structure and dielectric properties of poled <001>-oriented 0.7Pb($Mg_{1/3}Nb_{2/3})O_3-0.3PbTiO_3$ (PMN-0.3PT) crystals have been investigated for orientations both parallel and perpendicular to the [001] poling direction. An electric field induced monoclinic phase was observed for the initial poled sample. The phase remained stable after the field was removed. A quite different temperature dependence of dielectric constant has been observed between heating and cooling due to an irreversible phase transformation. The results of mesh scans and temperature dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a single domain tetragonal phase at 370K and to a paraelectric cubic phase at 405K upon heating. However, upon subsequent cooling from the unpoled state, the cubic phase changes to a poly domain tetragonal phase and to a rhombohedral phase. In the ferroelectric tetragonal phase with a single domain state, the dielectric constant measured perpendicular to the poling direction was dramatically higher than that of the parallel direction. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believed to be related to dielectric softening close to the morphotropic phase boundary and at the phase transition temperature.

Scanning Force Microscope에 의한 (001) PMN-x%PT 단결정의 도메인 구조에 대한 연구

이은구,이재갑,Lee, Eun-Gu,Lee, Jae-Gab 한국재료학회 2009 한국재료학회지 Vol.19 No.6

The domain structures of annealed (001)-oriented $Pb(Mg_{1/3}Nb_{2/3})O_3-x%PbTiO_3$ (PMN-x%PT) crystals for x = 10, 20, 30, 35, and 40 at% were investigated by Polarized Optical Microscopy (POM) and Scanning Force Microscopy (SFM) in the piezoresponse mode. Both Polar Nano-Domains (PND) and long strip-like domains were clearly observed. The results also showed how the domain structure changed between phases with an increasing x in the PMN-x%PT crystals and the domain hierarchy on various length scales ranging from 40 nm to 0.1 mm. Distorted pseudo-cubic phase (x < 20%) consisted of PNDs that did not self-assemble into macro-domain plates. The rhombohedral phase (x = 30%) consisted of PNDs that began to self-assemble into colonies along preferred {110} planes. The monoclinic phase (x = 35%) consisted of miniature polar domains on the nm scale, whereas, the tetragonal phase (x = 40%) consisted of {001} oriented lamella domains on the mm scale that had internal nano-scale heterogeneities, which self-assembled into macro-domain plates oriented along {001} the mm scale.

저압 화학 기상 증착법으로 제작한 다결정 실리콘의 표면 형태 및 결정 성장

이은구,박진성,이재갑,Lee, Eun-Gu,Park, Jin-Seong,Lee, Jae-Gap 한국재료학회 1995 한국재료학회지 Vol.5 No.2

The surface morphology and grain growth of amophous silicon (a-Si) films deposited by low pressure chemical vapor deposition (LPCVD) have been investigated as a function of deposition and in sltu annealing condition. The film deposited at the amorphous to polycrystalline transition temperature has an extra-rough, rugged surface with (311) t.exture. At the same deposition temperature, the grain structure tends to shirr. from the polycrystalline to the amorphous phase with increasing the film thickness. It is found that nucleation of a-Si during in situ annealing at the transition temperature without breaking the vacuum starts to occur from surface Si atom migration in contrast to a heterogeneous nucleation during film deposition.

단결정 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ 의 상전이에 미치는 전장의 영향

이은구,Lee, Eun-Gu 한국재료학회 2013 한국재료학회지 Vol.23 No.6

The structural phase transformations of $0.7Pb(Mg_{1/3}Nb_{2/3})O_3-0.3PbTiO_3$ (PMN-0.3PT) were studied using high resolution x-ray diffraction (HRXRD) as a function of temperature and electric field. A phase transformational sequence of cubic (C)${\rightarrow}$tetragonal (T)${\rightarrow}$rhombohedral (R) phase was observed in zero-field-cooled conditions; and a $C{\rightarrow}T{\rightarrow}$monoclinic $(M_C){\rightarrow}$ monoclinic ($M_A$) phase was observed in the field-cooled conditions. The transformation of T to $M_A$ phase was realized through an intermediate $M_C$ phase. The results also represent conclusive and direct evidence of a $M_C$ to $M_A$ phase transformation in field-cooled conditions. Beginning from the zero-field-cooled condition, a $R{\rightarrow}M_A{\rightarrow}M_C{\rightarrow}T$ phase transformational sequence was found with an increasing electric field at a fixed temperature. Upon removal of the field, the $M_A$ phase was stable at room temperature. With increasing the field, the transformation temperature from T to $M_C$ and from $M_C$ to $M_A$ phase decreased, and the phase stability ranges of both T and $M_C$ phases increased. Upon removal of the field, the phase transformation from R to $M_A$ phase was irreversible, but from $M_A$ to $M_C$ was reversible, which means that $M_A$ is the dominant phase under the electric field. In the M phase region, the results confirmed that lattice parameters and tilt angles were weakly temperature dependent over the range of investigated temperatures.

우수한 수렴특성을 갖는 3차원 열흐름 방정식의 이산화 방법

이은구,윤현민,김철성,Lee, Eun-Gu,Yun, Hyun-Min,Kim, Cheol-Seong 한국전기전자학회 2002 전기전자학회논문지 Vol.6 No.2

The simulator for the analysis of the lattice temperature under the steady-state condition is developed. The heat flow equation using the Slotboom variables is discretized and the integration method of the thermal conductivity without using the numerical analysis method is presented. The simulations are executed on the $N^+P$ junction diode and BJT to verify the proposed method. The average relative error of the lattice temperature of $N^+P$ diode compared with DAVINCI is 2% when 1.4[V] forward bias is applied and the average relative error of the lattice temperature of BJT compared with MEDICI is 3% when 5.0[V] is applied to the collector contact and 0.5[V] is applied to the base contact. BANDIS using the proposed method of integration of thermal conductivity needs 3.45 times of matrix solution to solve one bias step and DAVINCI needs 5.1 times of matrix solution MEDICI needs 4.3 times of matrix solution.