• JSTS:Journal of Semiconductor Technology and Science
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• 제17권2호
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• pp.265-270
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• 2017

4H-SiC has attracted attention for high-power and high-temperature metal-oxide-semiconductor field-effect transistors (MOSFETs) for industrial and automotive applications. The gate oxide in the 4H-SiC MOS system is important for switching operations. Above $1000^{\circ}C$, thermal oxidation initiates $SiO_2$ layer formation on SiC; this is one advantage of 4H-SiC compared with other wide band-gap materials. However, if post-deposition annealing is not applied, thermally grown $SiO_2$ on 4H-SiC is limited by high oxide charges due to carbon clusters at the $SiC/SiO_2$ interface and near-interface states in $SiO_2$; this can be resolved via low-temperature deposition. In this study, low-temperature $SiO_2$ deposition on a Si substrate was optimized for $SiO_2/4H-SiC$ MOS capacitor fabrication; oxide formation proceeded without the need for post-deposition annealing. The $SiO_2/4H-SiC$ MOS capacitor samples demonstrated stable capacitance-voltage (C-V) characteristics, low voltage hysteresis, and a high breakdown field. Optimization of the treatment process is expected to further decrease the effective oxide charge density.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.224-224
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• 2016

Many researchers have been tried to improve the performance of the phosphorescent organic light-emitting diode(PHOLED) by controlling of the dopant profile in the emission layer. In this work, as shown in Fig. 1 insert, a typical red PHOLED device which has the structure of ITO/NPB(50nm)/CBP(30nm)/TPBi(10nm)/Alq3(20nm)/LiF(0.8nm)/Al(100nm) is fabricated with a 5nm thick doping section in the emission layer. The doping section is formed by co-deposition of CBP and Ir(btp)2acac with a doping concentration of 8%, and it's location(x) is changed from HTL/EML interface to EML/HBL in 5nm steps. The current efficiency versus current density of the devices are shown in Fig. 1. By changing the location of doping section, as shown in Fig. 1 and 2, at x=5nm, the efficiency shows the maximum of 3.1 cd/A at 0.5 mA/cm2 and it is slightly decreased when the section is closed to HTL and slightly increased when the section is closed to HBL. If the doping section is closed to HTL(NPB) the excitons can be quenched easily to NPB's triplet state energy level(2.5eV) which is relatively lower than that of CBP(2.6eV). Because there is a hole accumulation at EML/HBL interface the efficiency can be increased slightly when the section is closed to HBL. Even the thickness of the doping section is only 5nm,. the maximum efficiency of 3.1 cd/A with x=5 is closed to that of the homogeneously doped device, 3.3 cd/A, because the diffusion length of the excitons is relatively long. As a result, we confirm that the current efficiency of the PHOLED can be improved by the doping profile optimization such as partially, not homogeneously, doped EML structure.

• 한국항공우주학회지
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• 제38권6호
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• pp.620-628
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• 2010

소형위성은 저비용으로 단기간에 개발이 가능하기 때문에 이를 통해 폭 넓은 우주 연구를 수행할 수 있고 다양한 분야의 활용 가능하다. 소형위성은 빠른 개발이 가능한 이점이 있다. 따라서 신속 대응 우주 구현이 주목됨에 따라 소형위성의 역할이 급속히 증가하고 있다. 하지만 소형위성은 기존의 위성에 비해 크기나 전력의 제약이 많기 때문에 고성능의 안정적인 시스템을 기대하기는 어렵다. 이러한 문제점을 해결하고 빠른 개발을 위해 표준화와 모듈화 설계가 필요하다. 모듈화는 플러그 앤 플레이(Plug-and-Play)를 지원하여 수일 내에 인공위성 제작 및 시험을 가능하게 한다. 이러한 모듈 간의 원활한 데이터 통신을 위해서는 데이터 버스의 표준이 요구된다. CAN 통신 방식은 플러그 앤 플레이에 가장 효과적으로 대처 할 수 있는 통신방식으로 꼽힌다. CAN은 높은 신뢰성을 가지며 분산 시스템을 지원하여 위성의 호환성을 높여준다. 따라서 시험이 용이해지고 짧은 기간에 고성능의 안정적인 위성 개발이 가능하게 된다. 본 논문에서는 모듈화 방식의 소형위성 개발 방안에 대해 제안하고, CAN을 데이터 버스로 적용하여 소형위성 내부 데이터 인터페이스 버스를 설계하고 시험을 통해 적합성을 분석하여 기술하였다.

• Coupled systems mechanics
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• 제5권2호
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• pp.191-201
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• 2016

Coupled structures are widely seen in civil and mechanical engineering. In coupled structures, monitoring the translational motion of its key components is of great importance. For instance, some coupled arms are equipped with a hydraulic piston to provide the stiffness along the piston axial direction. The piston moves back and forth and a distance sensing system is necessary to make sure that the piston is within its stroke limit. The measured motion data also give us insight into how the coupled structure works and provides information for the design optimization. This paper develops two distance sensing systems for coupled structures. The first system measures distance with ultrasonic sensor. It consists of an ultrasonic sensing module, an Arduino interface board and a control computer. The system is then further upgraded to a three-sensor version, which can measure three different sets of distance data at the same time. The three modules are synchronized by the Arduino interface board as well as the self-developed software. Each ultrasonic sensor transmits high frequency ultrasonic waves from its transmitting unit and evaluates the echo received back by the receiving unit. From the measured time interval between sending the signal and receiving the echo, the distance to an object is determined. The second distance sensing system consists of a wire draw encoder, a data collection board and the control computer. Wire draw encoder is an electromechanical device to monitor linear motion by converting a central shaft rotation into electronic pulses of the encoder. Encoder can measure displacement, velocity and acceleration simultaneously and send the measured data to the control computer via the data acquisition board. From experimental results, it is concluded that both the ultrasonic and the wire draw encoder systems can obtain the linear motion of structures in real-time.

• 한국위성정보통신학회논문지
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• 제11권2호
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• pp.23-28
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• 2016

본 논문에서는 ISM(Industry-Science-Medical) 대역의 와이파이-AP(Access Point)의 채널추정에 따라 스마트 미디어의 HDMI(High Definition Multimedia Interface) 해상도를 조정하고자 한다. 2.4/5GHz 대역에서의 채널모델은 RSSI(Received Signal Strength Indication)와 같은 RF특성에 따라 광범위하게 적용할 수 있다. 특별히, 스마트 디바이스의 증가와 무선 랜 공유기(AP)로 인한 동일채널 간섭으로 인한 와이파이의 전송 속도저하와 미디어 스트리밍의 화질저하가 발생된다. 이때 무선채널의 전송속도에 따라 HDMI-CEC(Consumer Electronics Control)를 활용한 동영상 비디오 형식(Video Format Timing)의 최적화를 설계한다. 이로서 스마트 다바이스와 DLNA(Digital Living Network Alliance) 등의 다양한 전송방식(Protocol)에 따라 홈 게이트웨이와 디지털TV 등의 HDMI 해상도를 가변적으로 조절하는 화질유지의 기법 및 PIP 위치설정 방법을 활용할 수 있다.

• 대한기계학회논문집A
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• 제31권5호
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• pp.609-616
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• 2007

Palletizing is necessary to promote the efficiency of storage and shipping tasks. These are, however some of the most monotonous, heavy and laborious tasks in the factory. Therefore many types of robot palletizing systems have been developed, but many robot motion commands still depend on the teaching pendent. That is, an operator inputs the motion command lines one by one. It is very troublesome, and most of all, the user must know how to type the code. That is why we propose a new GUI (Graphic User Interface) Palletizing System. To cope with this issue, we proposed a 'PLP' (Pallet Loading Problem) algorithm, Fast Algorithm and realize 3D auto-patterning visualization interface. Finally, we propose the robot palletizing simulator. Internally, the schematic of this simulator is as follows. First, an user inputs the physical information of object. Second, simulator calculates the optimal pattern for the object and visualizes the result. Finally, the calculated position data of object is passed to the robot simulator. To develop the robot simulator, we use an articulated robot, and analyze the kinematics and dynamics. Especially, All problem including thousands of boxes were completely calculated in less than 1 second and resulted in optimal solutions by the Fast Algorithm.

• 한국시뮬레이션학회논문지
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• 제20권1호
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• pp.107-116
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• 2011

최근 가정 또는 사무실과 같은 실내 환경에서 음영지역을 해소하고 고품질의 서비스 제공을 위한 방안으로 초소형 기지국인 펨토셀(Femtocell)이 많은 관심을 받고 있다. 펨토셀은 사업자 및 사용자에게 다양한 이점을 제공하지만 펨토셀의 도입을 위해 서는 채널 선택에 따른 간섭제어, 네트워크 동기화, 자기 최적화 등 다양한 기술적 문제점이 해결되어야 한다. 이를 위해 본 연구에서는 펨토셀의 도입으로 인하여 발생 가능한 다양한 신호간섭 문제들에 대한 분석을 용이하게 하기 위한 LTE(Long Term Evolution) 시스템 기반 펨토셀 시뮬레이터를 개발하였다. 개발된 시뮬레이터는 단말 이동성, 스케줄러, 호 수락 제어, 트래픽 생성, MCS(Modulation and Coding Scheme) 결정의 5개의 블록과 이를 연결하고 관리하는 메인 모듈로 구성되어 있다. 또한 사용자의 편의성을 도모하기 위하여 시뮬레이션 결과를 실시간으로 관측할 수 있는 GUI(Graphical User Interface)를 적용하였다. 본 시뮬레이터는 실제와 유사한 환경에서 매크로셀과 펨토셀 사이의 간섭영향을 면밀히 분석하고 이동통신 시스템의 성능을 효과적으로 평가할 수 있도록 지원하며, 다양한 펨토셀 시스템을 개발하는데 크게 기여할 수 있을 것으로 예상된다.

• Journal of the Optical Society of Korea
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• 제17권5호
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• pp.447-453
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• 2013

A micro zoom system without moving elements by use of two liquid lenses is designed and optimized in this paper. The zoom equations of the system composed of two liquid lenses are deduced. The structure parameters including radius and thickness of a conical double-liquid electrowetting based lens are analyzed and calculated. Because the liquid thickness varies non-linearly with the radius of the interface, it's very difficult to optimize a real liquid lens using commercial optical design software directly. Through the Application Programming Interface (API) of the optical design software CODE V, a zoom system with two real electrowetting based liquid lenses is modeled and optimized. A two-liquid-lens zoom system without moving elements, with a zoom factor of 1.8 and a compact structure of 10 mm is designed for illustration. This can be useful for the camera design of mobile phones, tablets and so on. And this paper presents a convenient way of designing and optimizing a zoom system including liquid lenses by commercial optical design software.

• 한국정보통신학회논문지
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• 제14권2호
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• pp.287-295
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• 2010

본 논문에서는 MPI(Message Passing Interface) 환경 하에서 채널배선 문제에 대한 분산 평균장 유전자 알고리즘(MGA, Mean field Genetic Algorithm)이라는 새로운 최적화 알고리즘을 제안한다. 분산 MGA는 평균장 어닐링(MFA, Mean Field Annealing)과 시뮬레이티드 어닐링 형태의 유전자 알고리즘(SGA, Simulated annealing-like Genetic Algorithm)을 결합한 경험적 알고리즘이다. 평균장 어닐링의 빠른 평형상태 도달과 유전자 알고리즘의 다양하고 강력한 연산자를 합성하여 최적화 문제를 효율적으로 해결하였다. 제안된 분산 MGA를 VLSI 설계에서 중요한 주제인 채널 배선문제에 적용하여 실험한 결과 기존의 GA를 단독으로 사용하였을 때보다 최적해에 빠르게 도달하였다. 또한 분산 알고리즘은 순차 알고리즘에서의 최적해 수렴 특성을 해치지 않으면서 문제의 크기에 대하여 선형적인 수행시간 단축을 나타냈다.

• 한국IT서비스학회지
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• 제14권3호
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• pp.183-196
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• 2015

The concept of energy-efficient networking has begun to spread in the past few years, gaining increasing popularity. A common opinion among networking researchers is that the sole introduction of low consumption silicon technologies may not be enough to effectively curb energy requirements. Thus, for disruptively boosting the network energy efficiency, these hardware enhancements must be integrated with ad-hoc mechanisms that explicitly manage energy saving, by exploiting network-specific features. The IEEE 802.3az Energy Efficient Ethernet (EEE) standard is one of such efforts. EEE introduces a low power mode for the most common Ethernet physical layer standards and is expected to provide large energy savings. However, it has been shown that EEE may not achieve good energy efficiency because mode transition overheads can be significant, leading to almost full energy consumption even at low utilization levels. Coalescing techniques such as packet coalescing and interrupt coalescing were proposed to improve energy efficiency of EEE, but their implementations typically adopt a simple policy that employs a few fixed values for coalescing parameters, thus it is difficult to achieve optimal energy efficiency. The paper proposes adaptive interrupt coalescing (AIC) that adopts an optimal policy that could not only improve energy efficiency but support performance. AIC has been implemented at the sender side with the Intel 82579 network interface card (NIC) and e1000e Linux device driver. The experiments were performed at 100 M bps transfer rate and show that energy efficiency of AIC is improved in most cases despite performance consideration and in the best case can be improved up to 37% compared to that of conventional interrupt coalescing techniques.