Improvement of <tex> $V_{\rm th}$</tex> Instability in Normally-Off GaN MIS-HEMTs Employing <tex> ${\rm PEALD}\hbox{-}{\rm SiN}_{\rm x}$</tex> as an Interfacial Layer

Woojin Choi,Hojin Ryu,Namcheol Jeon,Minseong Lee,Ho-Young Cha,Kwang-Seok Seo IEEE 2014 IEEE electron device letters Vol.35 No.1

<P>In this letter, reduction of threshold voltage instability in gate recessed normally-off GaN metal insulator semiconductor high electron mobility transistors with SiN<SUB>x</SUB> gate insulator was investigated. A plasma enhanced atomic layer deposition technique was successfully employed for very thin SiN<SUB>x</SUB> (5 nm) as an interfacial layer. The hysteresis and drift of threshold voltage in transfer curve and the forward biased gate leakage current were effectively reduced.</P>

Safe Navigation of a Mobile Robot Considering Visibility of Environment

Woojin Chung,Seokgyu Kim,Minki Choi,Jaesik Choi,Hoyeon Kim,Chang-bae Moon,Jae-Bok Song IEEE 2009 IEEE transactions on industrial electronics Vol.56 No.10

<P>We present one approach to achieve safe navigation in an indoor dynamic environment. So far, there have been various useful collision avoidance algorithms and path planning schemes. However, those algorithms possess fundamental limitations in that the robot can avoid only ldquovisiblerdquo ones among surrounded obstacles. In a real environment, it is not possible to detect all the dynamic obstacles around the robot. There are many occluded regions due to the limited field of view. In order to avoid collisions, it is desirable to exploit visibility information. This paper proposes a safe navigation scheme to reduce collision risk considering occluded dynamic obstacles. The robot's motion is controlled by the hybrid control scheme. The possibility of collision is dually reflected to path planning and speed control. The proposed scheme clearly indicates the structural procedure on how to model and to exploit the risk of navigation. The proposed scheme is experimentally tested in a real office building. The experimental results show that the robot moves along the safe path to obtain sufficient field of view. In addition, safe speed constraints are applied in motion control. It is experimentally verified that a robot safely navigates in dynamic indoor environment by adopting the proposed scheme.</P>

Development of the Low-Cost Impedance Spectroscopy System for Modeling the Electrochemical Power Sources

Woojin Choi,Juhyung Lee 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-

This paper presents a low-cost impedance spectroscopy system (LCISS) suitable for modeling the electrochemical power sources such as fuel cells, batteries and supercapacitors. Since the developed LCISS is composed of simple sensor circuits, commercial data acquisition board and software, it provides a low cost solution for modeling and diagnosing the electrochemical power sources compared with the commercial electrochemical impedance spectroscopy instruments. The system is capable of automatically measuring the impedance of the electrochemical power sources over the specified frequency range and from the measured impedance data an equivalent circuit can be derived by the developed software. In the proposed system, the digital lock-in amplification technique is adopted to achieve the accurate measurements even in the presence of the high level of noises. The validity of the developed system is proven by comparing the measured frequency response of a simple R-C filter with those obtained by using the commercial frequency response analyzer (NF FRA 5097). The developed hardware and software is applied to measure the impedance spectrum of the 1.2㎾ proton exchange membrane fuel cell and the results are detailed.

High-Voltage and Low-Leakage-Current Gate Recessed Normally-Off GaN MIS-HEMTs With Dual Gate Insulator Employing PEALD-<tex> ${\rm SiN}_{x}$</tex> /RF-Sputtered-<tex> ${\rm HfO}_{2}$</tex>

Woojin Choi,Ogyun Seok,Hojin Ryu,Ho-Young Cha,Kwang-Seok Seo IEEE 2014 IEEE electron device letters Vol.35 No.2

<P>To fabricate gate recessed normally-off AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors, we have employed a novel SiNx/HfO2 dual gate insulator. A plasma enhanced atomic layer deposition (PEALD) technique was used for very thin high quality SiNx (5 nm) as an interfacial layer followed by RF-sputtered HfO2 as a high- k dielectric for the second gate insulator structure. The PEALD SiNx interfacial layer effectively suppresses the forward gate leakage current and the current collapse. We have achieved excellent characteristics such as large threshold voltage of 1.65 V, high breakdown voltage of 900 V, extremely small off-state drain leakage current less than 10<SUP>-9</SUP> A/mm and high ON/OFF drain current ratio of ~ 10<SUP>9</SUP>, low on-state resistance of 1.84 mΩ·cm<SUP>2</SUP>, and small subthreshold slope of 85 mV/decade.</P>

Differential Autonomic Response to Acupuncture at Wood and Metal of Five-<i>Shu</i> Acupoints

Choi, Woojin,Lee, Seunggi,Cho, Seunghun,Park, Kyungmo Mary Ann Liebert 2012 The journal of alternative and complementary medic Vol.18 No.10

<P>The study examined differential autonomic nervous responses to acupuncture stimulation at the wood points ([Formula: see text]) and the metal points ([Formula: see text]) among the five-shu points of the Pericardium and Triple Energizer Meridian.</P>

On the Trail from DNA to Protein, Chasing the Butterfly Virus

Woojin Kim,Jae-Young Choi,Yeon-Ho Je 한국응용곤충학회 2014 한국응용곤충학회 학술대회논문집 Vol.2014 No.10

Nucleopolyhedrovirus (NPV), which belongs to Baculoviridae, is a rod-shaped, double-stranded circular DNA virus which infects arthropods, mostly insects. NPVs are highly species-specific, and make unique crystalline polyhedral structure made of polyhedrin protein. The NPVs do not replicate in mammalian cells, are safe to human, and can be observed the viral replication with conventional compound microscope, plus the availability of susceptible insect cell lines, therefore, the NPVs became an ideal model system to study basic virology. Also, NPVs became popular because of its applications for baculovirus expression vector system (BEVS). A foreign gene will be cloned into a shuttle vector, and introduced to the NPV chromosome to make recombinant virus. This NPV will produce the protein in culture cells or host insects under the control of the strong polyhedrin promoter. So far, the commercially available BEVS has been widely used because of its high efficiency and eukaryotic characteristics, however, the hidden bottleneck is finding new useful genes which will maximize the capability of BEVS. Since the human genome project, next generation sequencing technique (NGS) is getting useful in life science field along with the development of sequence analysis algorithms and increase of computational power. Especially, RNA-seq and de novo sequence assembly technics make discovery of new genes easier even in a non-model species with a proteomics approach, and these useful tools will be the key to catalyze the insect biotechnology.

Developing an AI-based automated fashion design system: reflecting the work process of fashion designers

Woojin Choi,Seyoon Jang,Ha Youn Kim,이유리,Sang-goo Lee,Hanbit Lee,Sungchan Park 한국의류학회 2023 Fashion and Textiles Vol.10 No.1

With the recent expansion of the applicability of artificial intelligence into the creative realm, attempts are being made to use AI (artificial intelligence) in the garment development system in various ways, both in academia and the fashion business. Several IT companies have developed and possess AI-based garment design technologies that utilize StyleGAN2 for image transformation. However, they are not widely utilized in the fashion business. Since fashion brands need to create numerous designs to launch new garment products for at least two seasons per year, the adoption of AI-based garment design generation technology can be one way to increase work efficiency. Therefore, this research aims to collect and analyze existing cases of AI-based garment design tools in order to identify the similarities and differences between the garment development processes of human designers and the existing AI-based garment design tools. Based on this analysis, the research aims to develop an AI-based garment development system that takes into consideration the garment development process of human designers, incorporating fashion domain knowledge.

Diffusion of fashion trend information: a study on fashion image mining from various sources

Woojin Choi,이유리,Seyoon Jang 한국의류학회 2024 Fashion and Textiles Vol.11 No.1

The advancement in the internet and mobile technologies has substantially altered information diffusion in modern society, creating a diverse environment for generating and sharing various forms of information. Specifically, the emergence of new information sources, such as influencers and online communities, has significantly influenced the formation of consumer opinion. We highlight the changes that have occurred in the diffusion of fashion trend information. To do this, we conducted data mining, which involved three main steps: data preprocessing, specifically converting image data (including images from the 2022 F/W season runway collection, fashion influencer outfits, and best items from online fashion retailers) into textual data; data mining analysis (quantitative analysis); and data post-processing. As a result, we found that even items with low or no appearance on the runway held significance in the best item data or fashion influencer outfits. Specifically, the best items on online fashion retailers, reflecting popular fashion trends, had greater similarity to fashion influencer outfits. However, similarities in silhouette attributes were found among runway collections, fashion influencer outfits, and best items data. This study holds great significance because it focuses on fashion items genuinely consumed by the mainstream consumers rather than only focusing on the four major runway collections. Furthermore, these findings offer valuable insights for merchandising and trend forecasting, emphasizing the importance of selectively utilizing fashion trend information in the planning of fashion products.

CNN 기반의 CAN 시스템 상의 악의적 노드 감지

정우진(Woojin Jeong),최은민(Eunmin Choi),한성민(Sungmin Han),최지웅(Ji-Woong Choi) 한국통신학회 2019 한국통신학회 학술대회논문집 Vol.2019 No.1

CAN에서의 자기상관 기반 침입 탐지 시스템

정우진(Woojin Jeong),최은민(Eunmin Choi),최지웅(Ji-Woong Choi) 제어로봇시스템학회 2021 제어·로봇·시스템학회 논문지 Vol.27 No.2

This paper proposes an autocorrelation-based intrusion detection system for a controller area network (CAN). The CAN is a bus topology network used in cyber-physical systems such as vehicles, robots, and trains. As the applications of the CAN are closely related to human life, and any malfunctions may lead to accidents, the system robustness is critical. However, the CAN is vulnerable to attacks because no authentication or encryption exists in the CAN protocol. The proposed system uses the autocorrelation of the CAN signals to identify the source node and detects the attack signals. Moreover, we evaluate the performance of the proposed system through a simulation and in a real-car environment. As the proposed system involves physical layer security, no modification of the CAN protocol is necessary. In addition, redundant security can be implemented when the system is applied with authentication or encryption protocols.