A model for I-V characteristics of GaAs MESFET's divided into three parts

기현철 漢陽大學校 大學院 1986 국내박사

O2O 서비스모델을 이용한 Homemade Food 서비스 모델

기현철 서울미디어대학원대학교 2017 국내석사

Sol-Gel법으로 製造된 (Ba Sr)TiO₃薄膜의 電氣的 特性에 관한 硏究

기현철 전남대학교 2000 국내석사

(Ba Sr)TiO₃thin-film capacitor has got such a high permittivity in practical temperature limits, a low loss factor and a little amount of the leakage current. Besides, its electrical property can be controlled by adjustment the component ratio of Sr. In this study, (Ba_xSr_(1-x))TiO₃(0.7≤x≤0.9) was coated on Pt/SiO₂/Si board by using Sol-Gel method. Coating process was repeated 3 times and then sintered at 750[℃] for 30 minutes. Each specimen was analyzed structure and electrical characteristics. In structure characteristics, EDX analyzed the samples ratio of the formation on the structural property. The result of EDX was 0.03[%] error for in the each samples. This error is considered to be occurred during the liquid was produced, by the impurities. Thermal behavior was observed with TG-DTA and concluded that the heat-treatment of the samples was degreed 750[℃]. Surface and section of thin films were observed with SEM. Growth of grain was well grown BST3. At that moment, size of grain was 50[nm] and thickness of the thin-film was about 2000∼2800[A]. The dielectric property, the permittivity and the loss factor to the frequency were 250 and 0.015 in BST3. The permittivity to the frequency showed diminution, and the loss factor increased a bit after decline when the frequency increased. The property of the leakage current was stable when the applied voltage was 0∼3[V] and increased in 4∼7[V]. And it reached to the insulation breakdown by increasing of the leakage current dramatically. The important feature of DRAM thin-film capacitor is the leakage current. This study was found very small amount of the leakage current in low voltage. It is considered to be applied to DRAM thin-film capacitor.

가출청소년의 실태 및 대책에 관한 연구

기현철 한세대학교 경찰법무대학원 2006 국내석사

Young people, who are carry the future of the country on their shoulders, are in an incomplete stage where they have not been completely socialized, and this is the reason why environmental factors surrounding them can have a number of effects such as mental damages caused by disappointment, depression, psychological conflict, and such when they should be growing up full of dreams and hopes. Matters concerning the runaway teenagers who are away from home wandering the streets and exposed to unacceptable environments as they are seceded from their family, school, and community out of destitution, poverty, violence, child abuse and abandonment, and maladjustment at school are rising as serious social problems. However, the access rate of runaway teenagers to protective service systems is very low as there is a serious lack in comprehensive protection and service system. Therefore, active measures such as deploying counseling and promotion personnel directly to the areas where there is a concentration of runaway teenagers and providing accurate informations about safe houses must be taken to aid runaway teenagers in getting access to protective service systems, and in order to increase the rate of early access to protective services, concentrated camping areas of runaway teenagers must be located, and through promotional activities such as providing guidance and information, connections with welfare services aimed at rehabilitating those who have returned from their seceded state must be expanded and high quality education must be made available so as to establish effective measures for protecting these teenagers. This thesis was written in order to contribute to protecting our teenagers who are the future of our country, and the purpose of this study is to show ways for reforming runaway teenagers, who are in important stages of their lives, based on results about factors which restrain behaviors that have to do with running away from home.

綠色有機發光素子의 高效率 및 壽命向上에 관한 硏究

기현철 전남대학교 대학원 2009 국내박사

Organic Light Emitting Device (OLED) has a characteristics to change the electric energy into the light when the electric field is applied to the organic material. OLED is currently employed as a light source for the lighting tools because research has progressed extensively the improvement of luminance and efficiency. OLED is widely used in the plate display device because of a simple manufacture process and high emitting efficiency. In this dissertation, Alq3 was used as a material to emit the green light in the green OLED and TPD in the HTL(Hole Transportation Layer) was used for the harmonious transportation of Hole. Also, LiF metal was utilized for ETL(Electron Transportation Layer) For the improvement of the emitting efficiency of green OLED, ITO surface was treated by using the RF plasma. Here, RF plasma power was changed to 25, 50, 100, and 200 W. Sheet resistance and surface roughness of ITO were measured after surface treatment. Sheet resistance of device treated with RF power of 25 W was 7.042 Ω/sq and surface roughness of device with RF power of 200 W was 2.438 nm. Green OLED was fabricated by using the substrate, which is ITO with surface treatment. Then, the electric and optical characteristics of green OLED were analyzed. The operating voltage was 5.5 V and luminance was 7,371 cd/m2 in case of RF power of 25 W. The measurement results were shown that the operating voltage was low because the work-function of ITO was increased when the sheet resistance of ITO was high. Here, the luminance and efficiency were enhanced by small surface roughness Also, we have proposed an Index matching film to improve the emitting efficiency of green OLED. Here, SiO2 and TiO2 were selected Index matching film coating material. The structures of Index matching film were designed in Glass/TiO2/SiO2/ITO and SiO2/TiO2/Glass/ITO. Then, these materials were deposited by ion-assisted deposition system. Transmittances of deposited devices were 86.14 and 85.07 %, respectively. These results show that the proposed structure has higher transmittance than the conventional ITO device. Luminances of green OLED with Glass/TiO2/SiO2/ITO and SiO2/TiO2/Glass/ITO structure were 15,400 and 13,000 cd/m2, respectively, at the applied voltage of 13.5 V. The measured luminances were increased by 1.5 and 2 times, respectively, in comparison with green OLED with surface treatment(7,370 cd/m2). In addition, these results were enhanced by 4.7 and 6 times, respectively, in comparison with green OLED without surface treatment(2,570 cd/m2). These results show that Index matching films have an effect on the improvement of efficiency and luminance of green OLED. In the research, we have proposed a novel encapsulation with simple process and steady film for external environment in comparison with conventional encapsulation method. This was designed to cover the emitting organic material from air. Silicon dioxide was used for thin film of encapsulation and the deposition thickness of the organic film was 220 nm. Operating voltage of green OLED with encapsulation was 5.5 V and luminance was 7.370 cd/m2 at the applied voltage of 14.5 V. Luminance was measured in 40 hour intervals at the air-exposed condition. After 400 hours, 1,000 hours, 1,600 hours and 2,000 hours, luminances of green OLED were 7,366, 7,200, 6,210 and 5,100 cd/m2, respectively. Luminance of green OLED doesn't decrease until 2,000 hours. As a results, proposed encapsulation can increase the life time of green OLED. 유기발광소자는 유기재료에 전계를 가하여 전기에너지를 빛으로 바꾸어주는 소자로서, 휘도 및 효율의 향상에 관련된 연구가 진행됨에 따라 조명기기용 광원으로 대체되고 있는 소자로 주목되고 있다. 또한 유기발광소자는 제작 공정이 간단하고 높은 발광효율을 나타내기 때문에 평판형 디스플레이 소자로 많이 이용되고 있다. 본 연구에서는 녹색유기발광소자의 발광층 물질로는 Alq3를 사용하였으며, 정공의 수송을 원활하기 위하여 정공수송층으로는 TPD를, 전자의 수송을 위하여 LiF를 사용하였다. 녹색유기발광소자의 효율을 향상시키기 위하여 양극으로 사용하는 ITO 표면을 RF plasma로 표면처리를 하였다. 이때, RF 플라즈마 출력은 25, 50, 100 및 200 W로 변화 시켰다. 표면 처리된 ITO 기판의 표면저항과 표면거칠기, 투과율을 측정했을 때, RF plasma power를 25 W로 처리한 소자의 표면 저항값이 7.042 Ω/sq으로 가장 높았으며, 표면거칠기는 200 W로 처리한 소자의 값이 2.438 nm로 우수한 특성을 나타냈다. 표면처리한 ITO 기판을 이용하여 녹색유기발광소자를 제작하였고, 전기 및 광학적 특성을 분석하였다. 플라즈마 출력이 25 W인 경우 동작전압은 5.5 V, 인가전압 14 V일 때 휘도는 7,371 cd/m2으로 우수하였다. 플라즈마 처리에 따른 ITO의 표면저항이 높은 값을 갖는 소자일수록 일함수 값이 증가하기 때문에 동작전압은 낮아지며, 표면거칠기 특성이 향상됨에 따라 휘도와 효율이 향상 될 수 있음을 알 수 있었다. 또한, 발광효율을 향상하기 위하여 Index matching film을 적용하였으며, 증착 물질로는 SiO2, TiO2를 선정하였다. Index matching film의 구조는 Glass/TiO2/SiO2/ITO 와 SiO2/TiO2/Glass/ITO 구조로 설계하여 증착하였다. 증착된 소자의 투과율을 측정하였으며, 각소자의 투과율은 각각 86.14 % 와 85.07 %로 일반적인 ITO(투과율 80%)보다 높은 투과율을 나타냈다. Glass/TiO2/SiO2/ITO 구조와 SiO2/TiO2/Glass/ITO 구조의 기판을 사용하여 제작된 녹색유기발광소자의 소자 휘도는 인가전압 13.5 V일 때 각각 15,400 cd/m2 와 13,000 cd/m2를 나타냈다. 표면처리하지 않는 소자의 휘도(2,570cd/m2)보다 Index matching film을 적용한 유기발광소자의 효율이 각각 약 6배와 약 2배 향상되었다. 또한, 표면 처리한 소자의 휘도는 7,370 cd/m2이므로 Index matching film을 적용한 유기발광소자의 효율이 각각 약 2배와 약 1.7배 향상되었다. 이상의 결과로부터 Index matching film이 유기발광소자의 휘도 향상과 효율 향상에 유효함을 알 수 있었다. 본 연구에서는 기존의 봉지방법과 비교하여 공정이 간단하고 실리콘 다이옥사이드 박막을 사용함으로써 외부 영향에 강한 녹색유기발광소자의 유기물층을 공기로부터 완전 보호 할 수 있도록 설계하였다. 봉지방식의 박막으로는 실리콘 다이옥사이드 박막을 이용하였으며, 증착두께는 녹색유기발광소자의 유기박막의 증착 두께인 220 nm을 증착하였다. 봉지방법을 적용하여 제작한 녹색유기발광소자의 동작전압은 5.5 V, 휘도는 인가전압이 14.5 V일 때 7,370 cd/m2를 나타냈다. 인가시간이 400, 1,000, 1,600 및 2,000시간 경과 후 각각의 휘도는 7,366, 7,200 6,210 및 5,100 cd/m2 나타낸 결과로 부터 시간이 경과함에 따라 밝기는 감소하는 것을 알 수 있었다. 그러나 단일박막을 적용하여 제작한 유기발광소자의 수명은 2,000시이간 지나도 초기의 휘도의 50 % 이상 유지함으로 소자의 수명은 약 2,000시간이 넘는 것으로 판단된다. 본 연구에서 제안된 단일 박막을 이용한 Encapsulation 방식은 유기발광소자의 수명향상을 할 수 있다고 판단된다.

논리레벨 변동을 보상하는 갈륨비소 베릿 다이오드 전계효과 트랜지스터 논리(BDFL)회로 설계에 관한 연구

기현철 漢陽大學校 1991 국내박사