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분극 엔지니어링을 통한 상시불통형 질화알루미늄갈륨 이종접합 전계효과 트랜지스터 설계
차호영,성혁기,Cha, Ho-Young,Sung, Hyuk-Kee 한국정보통신학회 2012 한국정보통신학회논문지 Vol.16 No.12
본 연구에서는 기존의 질화알루미늄갈륨/질화갈륨 이종접합 구조에서 강한 분극현상으로 인하여 구현하기 어려웠던 상시불통형 소자를 질화알루미늄갈륨 기판 혹은 버퍼층을 이용하여 구현하는 방법을 제안한다. 질화알루미늄갈륨 기판 혹은 버퍼층 위에 더 높은 Al 몰분율을 갖는 장벽층을 성장하고 최상부에 질화갈륨 층을 추가 성장하여 분극전하를 상쇄시키는 방법을 이용하여 선택적으로 게이트 아래의 채널만 공핍시켜 상시불통형 소자를 구현할 수 있다. 이를 통하여 본 연구에서는 상용 전력소자에서 요구하는 게이트 문턱전압 2 V 이상을 갖는 질화알루미늄갈륨 이종접합 전계효과 트랜지스터 에피구조를 제안한다. In this study, we propose a novel structure based on AlGaN substrate or buffer layer to implement a normally-off mode transistor that was difficult to be realized by conventional AlGaN/GaN heterojunction structures. The channel under the gate can be selectively depleted by growing an upper AlGaN barrier with a higher Al mole fraction and a top GaN charge elimination layer on AlGaN substrate or buffer layer. The proposed AlGaN heterojunction field effect transistor can achieve a threshold voltage of > 2 V, which is generally required in power device specification.
최적화 기법을 적용한 매체 이송 시스템의 이송속도 및 비틀어짐 제어기의 이득값 결정
차호영(Ho-Young Cha),범선호(Sun-Ho Bum),김민수(Min-Soo Kim),이순걸(Soon-Geul Lee) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.6
In this paper, we made a simple paper feeding system which is one of MTS (media transport system) and controllers. The plant has a flexible paper and two driving rollers and two driven rollers. The control system has two conventional PID controllers. Skew angle and feeding speed of MTS deteriorate the quality of feeding system. In order to control a feeding speed and skew of feeding paper, we control rotational velocity of two driving rollers. Therefore, this controller has two inputs and two outputs as MIMO (multi-input and multi-output) system. The control inputs were the feeding speed and the skew displacement of the paper. The control outputs were the rotational velocity to each driving roller. To find appropriate PID gains of two controllers, we proposed an optimization technique. We assume the system variables and performance of a whole system as follows. PID gains of two controllers for skew and feeding speed are system variables. System performance is both skew and feeding speed. We simulates to making mathematical correlation using global Kriging interpolation. To find appropriate value of system variables, optimization method is simulation in sequence as following method. First, the optimization solver simulates with DOE (design of experiment) tables to find correlation equation of both system variable and performances. Then, the solver guesses the appropriate values and simulates if the system variables are appropriate or not. If the result of validation doesn’t satisfy the convergence and iteration tolerance, the solver makes a new Kriging models and iterates this sequence until satisfy the tolerances.
플로팅 금속 가드링 구조를 이용한 Ga<sub>2</sub>O<sub>3</sub> 쇼트키 장벽 다이오드의 항복 특성 개선 연구
최준행,차호영,Choi, June-Heang,Cha, Ho-Young 한국전기전자학회 2019 전기전자학회논문지 Vol.23 No.1
본 연구에서는 TCAD 시뮬레이션을 사용하여 산화갈륨 ($Ga_2O_3$) 기반 수직형 쇼트키 장벽 다이오드 고전압 스위칭 소자의 항복전압 특성을 개선하기 위한 가드링 구조를 이온 주입이 필요 없는 간단한 플로팅 금속 구조를 활용하여 제안하였다. 가드링 구조를 도입하여 양극 모서리에 집중되던 전계를 감소시켜 항복전압 성능 개선을 확인하였으며, 이때 금속 가드링의 폭과 간격 및 개수에 따른 항복전압 특성 분석을 전류-전압 특성과 내부 전계 및 포텐셜 분포를 함께 분석하여 최적화를 수행하였다. N형 전자 전송층의 도핑농도가 $5{\times}10^{16}cm^{-3}$이고 두께가 $5{\mu}m$인 구조에 대하여 $1.5{\mu}m$ 폭의 금속 가드링을 $0.2{\mu}m$로 5개 배치하였을 경우 항복전압 2000 V를 얻었으며 이는 가드링 없는 구조에서 얻은 940 V 대비 두 배 이상 향상된 결과이며 온저항 특성의 저하는 없는 것으로 확인되었다. 본 연구에서 활용한 플로팅 금속 가드링 구조는 추가적인 공정단계 없이 소자의 특성을 향상시킬 수 있는 매우 활용도가 높은 기술로 기대된다. In this study, we have proposed a floating metal guard ring structure based on TCAD simulation in order to enhance the breakdown voltage characteristics of gallium oxide ($Ga_2O_3$) vertical high voltage switching Schottky barrier diode. Unlike conventional guard ring structures, the floating metal guard rings do not require an ion implantation process. The locally enhanced high electric field at the anode corner was successfully suppressed by the metal guard rings, resulting in breakdown voltage enhancement. The number of guard rings and their width and spacing were varied for structural optimization during which the current-voltage characteristics and internal electric field and potential distributions were carefully investigated. For an n-type drift layer with a doping concentration of $5{\times}10^{16}cm^{-3}$ and a thickness of $5{\mu}m$, the optimum guard ring structure had 5 guard rings with an individual ring width of $1.5{\mu}m$ and a spacing of $0.2{\mu}m$ between rings. The breakdown voltage was increased from 940 V to 2000 V without degradation of on-resistance by employing the optimum guard ring structure. The proposed floating metal guard ring structure can improve the device performance without requiring an additional fabrication step.
파일롯 규모 전기투석 막여과 시스템을 이용한 비소와 망간오염 지하수 처리
최수영 ( Su Young Choi ),권민욱 ( Min Wook Kwon ),박기영 ( Ki Young Park ),차호영 ( Ho Young Cha ),김희준 ( Hee Jun Kim ),권지향 ( Ji Hyang Kweon ) 한국물환경학회 2017 한국물환경학회지 Vol.33 No.3
A pilot-scale electrodialysis system was designed and constructed to treat groundwater polluted with arsenic and manganese. Synthetic groundwater, in which some amount of arsenic (As) and manganese (Mn) were added to a final concentration of 500 mg/L of Mn and 50 pg/L of As, was used as a feed for the ED system. The limiting current density, linear water velocity, applied voltage, and membrane surface area were investigated to obtain the efficient and economic operation of the ED system. The linear water velocity increased from 0.74 cm/s to 1 lcm/s, based on the evaluation of limiting current density. Using the ED system with 14 pairs of ion exchange membranes, the water quality of the diluate after 85 minutes of operation satisfied the water quality criteria for drinking water. Increasing the membrane pairs to 21 and 42 pairs was effective in reducing the conductivities of the diluate. The operation cost of the ED system was assessed using specific energy consumption, which was 1.065~ 1.2 kWli/m3. Considering low salt concentrations of the groundwater, increases in current utilization and low voltage applications are required when the ED system is used to produce drinking water.