• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.735-738
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• 2003

Downsizing electronics requires precision position control with an accuracy of sub-micron order, which demands development of ultra-fine displacive devices. Piezoelectric transducer is one of devices transferring electric field energy into mechanical energy and being capable for fine displacement control. The transducer has been widely used as fine Position control device Multilayer piezoelectric actuator, one of typical piezo-transducer, is fabricated by stacking alternatively ceramic and electrode layers several hundred times followed by cofiring process. Electrode material should be tolerable in the firing process maintaining at ceramic-sintering temperatures up to $1100{\sim}1300^{\circ}C$. Ag-Pd can be used as stable electrode material in heat treatment above $960^{\circ}C$. Besides, adding small quantity ceramic powder allow the actuator to be fabricated in a good shape by diminishing shrinkage difference between ceramic and electrode layers, resulting in avoidance of crack and delamination at and/or nearby interface between ceramic an electrode layers. This study presents synthesis of nano-oxide-added Ag/Pd powders and its feasibility to candidate material tolerable at high temperature. The powders were formed in a co-precipitation process of Ag and Pd in nano-oxide-dispersed solution where Ag and Pd precursors are melted in $HNO_3$ acid.

• 대한전자공학회논문지SD
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• 제39권4호
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• pp.84-92
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• 2002

최근의 FPGA는 매우 높은 집적도와 빠른 동작속도 때문에 많은 응용분야에서 널리 사용되고 있다. 그러나, FPGA에 구현된 설계를 디버깅하는 과정은, FPGA의 내부에 존재하는 수많은 신호선들을 탐침하는 과정이 매우 오랜 시간을 요하는 FPGA 재-컴파일을 최소 수 차례 이상 필요로 함으로서 많은 문제점을 가지고 있다. 본 논문에서는, 이와 같은 FPGA 디버깅의 문제점을 분석하고, 새로운 디버깅 방법을 제안한다. 제안되는 방법은 FPGA 내부에 존재1차는 모든 신호선들에 대한 100% 탐침을 한 차례의 FPGA 재-컴파일과정 없이도 수행하는 것을 가능하게 할 뿐만 아니라, 한번의 FPGA 컴파일 과정으로 최소 한 개의 설계 오류를 찾을 수 있도록 한다. 본 논문에서 제안된 방법은 실험을 통하여서도 매우 효과적이며 실용적임이 확인되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.331-332
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• 2006

Ag-ceramic composite materials were investigated as internal electrodes for multilayer ceramic actuators (MLCA). Ag-ceramic pastes were prepared by adding PZT-based ceramic powders to a Ag patse in a range of 0 to 50 wt.%. PZT/Ag-PZT multilayered laminates were fabricated by tape casting and fired at low temperatures below $950^{\circ}C$. The addition of ceramic into the Ag electrode resulted in a decrease in the thermal expansion mismatch between the electrode and the ceramic sheet. The maximum strain of PZT/Ag-PZT multilayered actuators were $9{\times}10^{-4}$ under an electric field of 2.5MV/m. In conclusion, Ag-PZT composite materials are efficient for low cost piezoelectric MLCAs.

• 한국재료학회지
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• 제27권1호
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• pp.48-52
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• 2017

In this study, we used I-V spectroscopy, photoconductivity (PC) yield and internal photoemission (IPE) yield using IPE spectroscopy to characterize the Schottky barrier heights (SBH) at insulator-semiconductor interfaces of Pt/$HfO_2$/p-type Si metal-insulator-semiconductor (MIS) capacitors. The leakage current characteristics of the MIS capacitor were analyzed according to the J-V and C-V curves. The leakage current behavior of the capacitors, which depends on the applied electric field, can be described using the Poole-Frenkel (P-F) emission, trap assisted tunneling (TAT), and direct tunneling (DT) models. The leakage current transport mechanism is controlled by the trap level energy depth of $HfO_2$. In order to further study the SBH and the electronic tunneling mechanism, the internal photoemission (IPE) yield was measured and analyzed. We obtained the SBH values of the Pt/$HfO_2$/p-type Si for use in Fowler plots in the square and cubic root IPE yield spectra curves. At the Pt/$HfO_2$/p-type Si interface, the SBH difference, which depends on the electrical potential, is related to (1) the work function (WF) difference and between the Pt and p-type Si and (2) the sub-gap defect state features (density and energy) in the given dielectric.

• Smart Structures and Systems
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• 제30권3호
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• pp.221-237
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• 2022

This paper is concerned with nonlinear modeling and efficient numerical simulation of electrostrictive materials and structures. Two types of such materials are considered: relaxor ferroelectric ceramics and electrostrictive polymers. For ceramics, a geometrically linear formulation is developed, whereas polymers are studied in a geometrically nonlinear regime. In the paper, we focus on constitutive modeling first. For the reversible constitutive response under consideration, we introduce the augmented Helmholtz free energy, which is composed of a purely elastic part, a dielectric part and an augmentation term. For the elastic part, we involve an additive decomposition of the strain tensor into an elastic strain and an electrostrictive eigenstrain, which depends on the polarization of the material. In the geometrically nonlinear case, a corresponding multiplicative decomposition of the deformation gradient tensor replaces the additive strain decomposition used in the geometrically linear formulation. For the dielectric part, we first introduce the internal energy, to which a Legendre transformation is applied to compute the free energy. The augmentation term accounts for the contribution from vacuum to the energy. In our formulation, the augmented free energy depends not only on the strain and the electric field, but also on the polarization and an internal polarization; the latter two are internal variables. With the constitutive framework established, a Finite Element implementation is briefly discussed. We use high-order elements for the discretization of the independent variables, which include also the internal variables and, in case the material is assumed incompressible, the hydrostatic pressure, which is introduced as a Lagrange multiplier. The elements are implemented in the open source code Netgen/NGSolve. Finally, example problems are solved for both, relaxor ferroelectric ceramics and electrostrictive polymers. We focus on thin plate-type structures to show the efficiency of the numerical scheme and its applicability to thin electrostrictive structures.

• 한국세라믹학회지
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• 제55권2호
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• pp.166-173
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• 2018

In order to investigate the effect of Mn on the dielectric and piezoelectric properties of PMN-PT [$Pb(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3$], four different types of 71PMN-29PT samples were prepared using the solid-state single crystal growth (SSCG) method: (1) Undoped single crystals, (2) undoped polycrystalline ceramics, (3) Mn-doped single crystals, and (4) Mn-doped polycrystalline ceramics. In the case of single crystals, the addition of 0.5 mol% Mn to PMN-PT decreased the dielectric constant ($K_3{^T}$), piezoelectric charge constant ($d_{33}$), and dielectric loss (tan ${\delta}$) by about 50%, but increased the coercive electric field ($E_C$) by 50% and the electromechanical quality factor ($Q_m$) by 500%, respectively. The addition of Mn to PMN-PT induced an internal bias electric field ($E_I$) and thus specimens changed from piezoelectrically soft-type to piezoelectrically hard-type. This Mn effect was more significant in single crystals than in ceramics. These results demonstrate that Mn-doped 71PMN-29PT single crystals, because they are piezoelectrically hard and simultaneously have high piezoelectric and electromechanical properties, have great potential for application in fields of SONAR transducers, high intensity focused ultrasound (HIFU), and ultrasonic motors.

• JSTS:Journal of Semiconductor Technology and Science
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• 제12권4호
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• pp.467-472
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• 2012

In this paper, we present a finite element method (FEM) study on the space charge effects in organic light emitting diodes. The physical model covers all the key physical processes in OLEDs, namely charge injection, transport and recombination, exciton diffusion, transfer and decay as well as light coupling, and thin-film-optics. The exciton model includes generation, diffusion, and energy transfer as well as annihilation. We assumed that the light emission originates from oscillation which thus is embodied as exciton in a stack of multilayer. We discuss the accumulation of charges at internal interfaces and their signature in the transient response as well as the electric field distribution. We also report our investigation on the influence of the insertion of the emission layer (EML) in the bilayer structure.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.787-790
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• 2001

Polymer bushing used for overhead line switch was designed and investigated. Requirements of electrical ratings such as partial discharge, ac withstand voltage, impulse voltage and material properties were proposed in accordance with IEEE 386 and pre-standard (PS) 151-146∼147, 170∼180 of KEPCO. The polymer bushing consists of an internal epoxy bushing and external housing made of EPDM rubber. The rubber housing was molded with mold cone. Therefore, the polymer bushing offers several advantages like light weight, good sealing properties, easy installation and excellent performance in contamination. Electric field analysis was also introduced in order to verify the reliability of the design.

• Journal of the Optical Society of Korea
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• 제8권1호
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• pp.34-52
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• 2004

Over the past decade the experimental technique of THz time domain spectroscopy (㎔- TDS) has proved to be a versatile method for investigating a wide range of phenomena in the ㎔ or far infrared spectral region from 100 ㎓ to 5 ㎔. This paper reviews some recent results of the Ultrafast ㎔ Research Group at Oklahoma State University using ㎔-TDS as a characterization tool. The experimental technique is described along with recent results on ㎔ beam propagation and how ㎔ beam profiles arise from propagation of pulse fronts along caustics. To illustrate how spatio-temporal electric field measurements can determine material properties over a wide spectral range, propagation of ㎔ pulses through systems exhibiting frustrated total internal reflection (FTIR) are reviewed. Finally two potential metrology applications of ㎔-TDS are discussed, thin film characterization and non-destructive evaluation of ceramics. Although ㎔-TDS has been confined to the research laboratory, the focus on application may stimulate the adoption of ㎔- TDS for industrial or metrology applications.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.594-597
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• 2003

In the present study, the piezoelectricity and polarization of multilayer ceramic actuator, being designed to stack PMN-PZ-PT ceramic layers and Ag-Pd electrode layers alternatively, were investigated under a consideration of geometric factor, the volume ratio of the ceramic to the electrode layers. The actuators were fabricated by tape casting of 0.2Pb(Mg1/3Nb2/3)O3-0.38PbZrO3-0.42PbTiO3 followed by lamination and burnout & co-firing processes. The actuators of 10 10 0.62 nm3 in size were formed in a way that 60 200 m thick ceramics were stacked alternatively with 5 m thick electrode layer. Increases in polarization and electric field-induced displacement with thickness of the ceramic layer were attributed to change of 90o/180o domain ratio, which was affected by interlayer internal stress. The piezoelectricity and actuation behaviors were found to depend upon the volume ratio (or thickness ratio) of ceramic to electrode layers.