• 한국세라믹학회지
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• 제55권1호
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• pp.67-73
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• 2018

A poled lead zirconate titanate (PZT) cube specimen that is switched by an electric field at room temperature is subject to temperature increase. Changes in polarization and thermal expansion coefficients are measured during temperature rise. The measured data are analyzed to obtain changes in pyroelectric coefficient and strain during temperature change. Empirical formulae are developed using linear or quadratic curve fitting to the data. The nonlinear behavior of the materials during temperature increase is predicted using the developed formulae. It is shown that the calculation results can be compared successfully with the measured values, which proves the accuracy and reliability of the developed formulae for the nonlinear behavior of the materials during temperature changes.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.763-766
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• 2000

In this paper, stator form-winding sample coils based on silicone resin and polyimide were made for fault prediction and reliability estimation on the 200 Class insulation system of traction motors. The complex accelerative degradation was performed by periods during 10 cycles, which was composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, condition diagnosis test such as insulation resistance & polarization index, capacitance & dielectric loss and partial discharge properties were investigated in the temperature range of 20∼160$^{\circ}C$. Relationship among condition diagnosis test was analyzed to find an dominative degradation factor and an insulation state at end-life point.

• 한국전기전자재료학회논문지
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• 제32권1호
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• pp.20-24
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• 2019

Ferroelectric material properties are strongly governed by domain structures and their evolution processes, but the evolution processes of complex domain patterns during a macroscopic electrical poling process are still elusive. In the present work, domain-evolution processes in a PZT ceramic near the morphotropic phase-boundary composition were studied during a step-wise electrical poling using piezoresponse force microscopy (PFM). Electron backscatter diffraction was used with the PFM data to identify the grain boundaries in the region of interest. In response to an externally the applied electric field, growth and retreat of non-$180^{\circ}$ domain boundaries wasere observed. The results indicate that ferroelectric polarization-switching nucleates and evolves in concordance with the pattern of the pre-existing domains.

• Coupled systems mechanics
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• 제10권6호
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• pp.521-544
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• 2021

In this work, we present the development of a 3D lattice-type model at microscale based upon the Voronoi-cell representation of material microstructure. This model can capture the coupling between mechanic and electric fields with non-linear constitutive behavior for both. More precisely, for electric part we consider the ferroelectric constitutive behavior with the possibility of domain switching polarization, which can be handled in the same fashion as deformation theory of plasticity. For mechanics part, we introduce the constitutive model of plasticity with the Armstrong-Frederick kinematic hardening. This model is used to simulate a complete coupling of the chosen electric and mechanics behavior with a multiscale approach implemented within the same computational architecture.

• 한국전자파학회논문지
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• 제15권11호
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• pp.1090-1099
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• 2004

본 논문에서는 PIN 다이오드의 on/off특성을 이용해 공진 주파수가 변하는 정삼각형 마이크로스트립 안테나를 제안하였다. PIN 다이오드가 off 상태에서는 T 형태 스퍼라인(Spur-line)의 영향으로 스퍼라인 주위로 전류가 돌아서 흐르기 때문에 안테나의 공진 주파수가 1.22 GHz를 보였으나, PIN 다이오드가 on상태일 때는 T형의 스퍼라인이 I 형태 슬롯라인(Slot-line)으로 바뀌고, 이 I 형태의 슬롯라인에 의해 전류가 영향을 덜 받아서 안테나의 공진 주파수가 1.82 GHz를 나타내었고, 이는 일반적인 정삼각형 마이크로스트져 안테나와 공진 주파수와 차이가 거의 없었다. 제안한 안테나는 PIN다이오드가 on, off상태에서 모두 교차 편파가 -20 dB미만의 방사패턴을 가진 선형 편파 특성을 나타내었다.

• 한국재료학회지
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• 제11권11호
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• pp.960-964
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• 2001

$Bi_{3.99}Ti_{2.97}V_{0.03}O_{12}$ (BTV) thin films with 3 mol% vanadium doping were Prepared on $Pt/Ti/SiO_2/Si$ substrate by sol-gel method. X-ray diffraction analysis indicated that single-phase layered perovskite were obtained and preferred orientation was not observed. Under the annealing temperature at $600^{\circ}C$, the surface morphology of the BTV thin films had fine-rounded particles and then changed plate-like at $650^{\circ}C$ and $700^{\circ}C$. The remanent polarization $(2P_r)$ and coercive field $(2E_c)$ of $700^{\circ}C$ annealed BTV thin film were 25 $\mu$C/cm$^2$ and 116 kV/cm, respectively. In addition, BTV thin film showed little polarization fatigue during $10_9$ switching cycles. These improved ferroelectric properties were attributed to the increased rattling space and reduced oxygen vacancies by substitution $Ti^{4+}$ ion (68 pm) with smaller $V^{5+}$ ion (59 pm). The dielectric constant and loss were measured 130 and 0.03 at 10 kHz, respectively.

• 한국전자파학회논문지
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• 제21권1호
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• pp.46-52
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• 2010

본 논문에서는 비대칭 십자형 접지면 슬롯 구조를 갖는 원형 편파 마이크로스트립 안테나와 접지면 슬롯 구조를 재구성하여 편파 특성을 변환시키는 방안을 제안하였다. 접지면의 슬롯 구조에 의해 방사 소자의 전류 흐름이 교란되어 원형 편파가 발생되며, PIN 다이오드의 on/off 동작 상태를 조정하여 비대칭 십자형 슬롯의 구조를 대칭적으로 변환시켜 원형 편파 특성을 재구성할 수 있다. 제안된 안테나는 원형 편파 형성을 위한 perturbation이 접지면에 위치하므로, PIN 다이오드 상태 조정을 위한 바이어스 회로 또한 접지면에 위치하게 되어 구현의 복잡도가 낮아지며, 이로 인해 방사 패턴의 왜곡을 감소시킬 수 있다. 제안된 안테나는 2.4 GHz 대역의 동작 주파수에서 임피던스 대역폭 150 MHz, 축비 대역폭 35 MHz, 최대 안테나 이득 1.7 dBi의 특성을 나타내었다.

• 한국진공학회지
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• 제11권4호
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• pp.230-234
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• 2002

고온 급속 열처리를 행한 $LiNbO_3Si$/(100) 구조를 가지고 여러 가지 전극을 사용하여 금속/강유전체/반도체 커패시터를 제작하였으며, 제작한 커패시터의 비휘발성 메모리 응용 가능성을 확인하였다. MFS 커패시터의 C-V 특성 곡선에서는 LiNbO$_3$박막의 강유전성으로 인한 히스테리시스 특성이 관측되었으며, 1 MHz C-V 특성 곡선의 축적 영역에서 산출한 비유전율은 약 25 이었다. Pt 전극을 사용하여 제작한 커패시터에서는 인가 전계 500 kV/cm 범위에서 $1\times10^{-8}$ A/cm 이하의 우수한 누설전류 특성이 나타났다. midgap 부근에서의 계면 준위 밀도는 약 $10^{11}\textrm{cm}^2$.eV 이었으며, 잔류분극 값은 약 1.2 $\muC/\textrm{cm}^2$ 였다. Pt 전극과 A1 전극 모두 500 kHz 주파수의 바이폴러 펄스를 인가하면서 측정한 피로 특성에서 $10^{10}$ cycle 까지 측정된 잔류 분극 값이 초기 값과 같았다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.504-508
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• 2003

New banana-shaped achiral compounds, 4-chloro-1,3-phenylene bis [4-4(3-fluoro-9-alkenyloxy) phenyl-iminomethylbenzoate]s and 4-chloro-1,3-phenylene bis [4-4-(3-fluoro-10-alkanyloxy) phenyliminomethyl benzoate]s were synthesized by varying the substituent (X=H, F, or Cl); their electrooptical properties are described. The smectic phases, including a switchable chiral smectic C ($SmC^{\ast}$) phase, were characterized by differential scanning calorimetry, polarizing optical microscopy, and triangular method. The presence of vinyl end group at the terminals of linear side wings in the banana-shaped molecules induced a decrease in melting temperature. The smectic phase having the undecenyloxy group such $as-(CH_2)_9CH=CH_2$ showed ferroelectric switching, and its value of spontaneous polarization on reversal of an applied electric field was 2250 $nC/cm^2$, while the value of spontaneous polarization of the smectic phase having the decanyloxy group such as $-(CH2)_9CH_3$ was 3700 $nC/cm^2$. We could obtain the ferroelectric phase with low isotropic temperature by varying the end group at the terminals of linear side wings in the banana-shaped achiral molecules.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.310-311
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• 2008

We have studied electro-optical characteristics of fringe-field switching (FFS) mode with high $d{\Delta}n$ according to the electrode position. In this device, the fringe-electric field drives the LCs to rotate so that the dielectric torque is electrode-positional dependent, which results in electrode-position dependency in the LC's rotating angle. We confirmed polarization microscope image and chromaticity diagram at the different electrode position with LC that have high $d{\Delta}n$. Since the FFS mode is influenced by horizontal and vertical electric field, the FFS mode modulates light using both phase retardation and polarization rotation effect, which had already been verified with previous studies. However, from another point of view, tight modulation of FFS mode has been demonstrated by performing experiment and calculated simulation at the high $d{\Delta}n$ LC cell.