• 한국세라믹학회지
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• 제54권4호
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• pp.261-271
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• 2017

Environment-friendly $(K,Na)NbO_3-based$ (KNN) lead-free piezoelectric materials have been studied extensively in the past decade. Significant progress has been made in this field, manifesting competitive piezoelectric performance with that of lead-based, for specific application scenarios. Further understanding of the relationship between high piezoelectricity and microstructure or more precisely, ferroelectric domain structure, domain wall pinning effect, domain wall conduction and local polarization switching underpins the continuous advancement of piezoelectric properties, with the help of piezoresponse force microscopy (PFM). In this review, we will present the fundamentals of scanning probe microscopy (SPM) and its cardinal derivative in piezoelectric and ferroelectric world, PFM. Some representative operational modes and a variety of recent applications in KNN-based piezoelectric materials are presented. We expect that PFM and its combination with some newly developed technology will continue to provide great insight into piezoelectric materials and structures, and will play a valuable role in promoting the performance to a new level.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.1123-1125
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• 2002

In this paper, interleaved boost converter is applied as a pre-regulator in switch mode power supply. Interleaved Boost Power Factor Preregulator (IBPFP) can reduce input current ripple as a simple voltage control loop only without inner current loop, because input current is divided each 50% by two switching devices. IBPFP can be classified as three cases from duty ratio condition in continuous current mode and be carried out state space averaging small signal modeling. According to modeling, the PID controller is applied and voltage control loop is constructed for suitable design condition. From frequency domain analysis, it is verified that control system is satisfied with design condition of switch mode power supply.

• 한국결정성장학회지
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• 제14권4호
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• pp.151-154
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• 2004

Issues of ferroelectric high-density memories (>64 Mb) indispensable for upcoming ubiquitous era have been on the cell integration less than $0.1\;\mu\textrm{m}^2$ and reliabilities. Thus nanoscale control of microstructures of ferroelectric films with large switching polarization has been one of the issues to obtain the uniform electrical properties for realization of high-density memories. In this study the grain orientations and distributions of BT-based films by spin-on coatings were examined by FEG-SEM/EBSD. Ferroelectric domain characteristics by PFM were also performed to study the dependence of reliabilities on the grain orientations and distributions. It is believed that understandings of the nucleation and growth mechanisms of the a- or b-axis oriented films during the thermal processes such as RTA and furnace annealing affecting on grain orientation and uniformity could be possible based on our experimental results.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -1
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• pp.70-73
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• 2002

High frequency digital LSI circuits are usually composed of many sub-circuits coupled with interconnects. They sometimes causes serious problems of the fault switching by time-delays, crosstalks, reflections of signals and so on. Therefore, it is very important to develop a user-friendly simulator for solving these problems. Although a moment matching method is widely used as the reduction technique of interconnects, it may happen to arise erroneous results for evaluating the poles far from the origin. In this paper, we show an asymptotic method in the complex frequency-domain, where we calculate the exact poles and residues giving large effect to the transient responses. Then, the interconnects are replaced by the asymptotic equivalent circuits using the poles and residues. Thus, we can develop a users-friendly simulator using the equivalent circuits.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.19-22
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• 2004

A 30-inch WQXGA+ TFT-LCD Monitor has been developed based on in-plane switching mode with multi-domain. This product adopts Cu electrode which, in spite of low resistivity, was not applied to TFT LCD products because of productivity and reliability problems etc. This low resistivity material makes it possible to clear the problem caused by line delay in such high resolution TFT-LCDs. As a results of successful adoption of innovative materials and technologies, our world's largest TFT-LCD Monitor has best performance for high information display.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.205-208
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• 2004

The switching mechanism of multi-domain vertical alignment mode LCD and delayed on response time phenomenon in special conditions are investigated. A modified DCC (Dynamic Capacitance Compensation), DCCII has been developed for the fast response time performance in PVA TFT-LCD TVs. DCCII applies a pre-tilt voltage to addressed pixels during the previous frame in addition to an overshoot voltage. In result, the response time less than 8 msec, has been obtained for all moving images through the DCCII technique.

• 인포메이션 디스플레이
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• 제5권5호
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• pp.4-9
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• 2004

최근 비오이 하이디스에서는 무제한의 광시야각과 시야각에 따른 색변화가 최소화된 선명한 색 특성을 갖는 Advanced FFS(Fringe Field Switching) 기술을 개발하였다. 이 기술은 resin 기술적용(평탄화에 의한 고개구율)없이 종래의 FFS 기술에서 액정의 전기 광특성을 최적화하는 새로운 디자인 룰을 찾아내어 실현하였다. 진보된 화소 개념은 전극의 모서리 구조, 전극 간격/폭, 칼라 필터의 블랙 마트릭스(BM)와 전극 간격등의 key parameters들의 최적화에 의해 달성되었고 액정 셀 내의 모서리와 전기장등이 액정을 미세하게 조정할 수 있도록 있게 된 것이다. 이러한 진보된 설계 개념은 모든 FFS 제품에 반영되어 개발되었다. 뿐만 아니라 12.1" XGA 제품에서 투과율이 22% 증가하고 흑백 대비비(Contrast Ratio)는 33% 증가한 600 : 1의 세계 최고 사양을 갖는 제품을 개발하게 되었다. 특히 태블릿과 노트북용 TFT- LCD 모듈에서 단일 도메인(Single Domain) 모드로도 White상태에서 시야각에 따른 색변화가 0.02 이하의 특성을 갖고 180도/180도의 무제한 시야각을 갖고 있다. Advanced FFS 기술의 브랜드 이름과 슬로건으로 'Viewiz'와 'Vision Magic'을 정하여 마케팅 중이며 세계적인 Top Tier 고객에 제품을 판매 중이고, 2004년 3분기에는 태블릿 시장에서 점유율 70%로 1위를 차지하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.247-250
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• 1991

In this paper, we have investigated the poling conditons depending upon the electric field and temperature for PZT ceramics with various stoichiometry prepared by wet direct method, and $MnO_2$ dopant. The electric field required for saturation polarization was plotted against temperature $(1,000/T^{\circ}K)$ so that the required field could be estimated at any given temperature by measuring the charge displaced during poling. From this curve it should be possible to predict the field required to produce maximum domain switching at temperature below the Curie temperature, when $MnO_2$ dopant was added to the PZT ceramics, the electric field required for saturation polarization was lowered than that of undoped PZT samples.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.508-511
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• 1991

In this paper, we have analyzed the transient and steady state characteristics of buck type DC-DC converter using the sliding mode control method based upon VSS. This control method provides the easier analysis tool due to the time domain analysis and the acquirement of desired transient characteristics if the slope of the switching line is properly selected, and guarantees the robustness against parameter uncertainties and load disturbances. Also, it can achieve direct nonlinear control without linearizing approximation of state space averaging method. PSPICE simulation results are then presented verifying these concepts.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2007년도 학술대회
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• pp.354-358
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• 2007

This article presents several methods of mobile communication network to access technologies utilizing unlicensed spectrum interworking. Generic Access Network (GAN) technology was already specified in GERAN (GSM EDGE Radio Access Network) and Interworking WLAN (I-WLAN) was standardized for WCDMA system for WLAN user to access WCDMA packet based services through WLAN access point. Voice Call Continuity is not access network dependent technology but is a kind of domain change scheme for voice call from Circuit Switching (CS) network to IP Multimedia Subsystem (IMS) and vice versa.