헤드램프 습기 해석을 위한 구조물 수분 방출 모델의 개발

최봉근(Bong Keun Choi),이철우(Chul Woo Lee),김억(Ok Kim) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

보도 사장교의 지진격리를 위한 면진받침 최적화

최봉근(Choi, Bong Keun),박장호(Park, Jang Ho),신영석(Shin, Young seok) 대한토목학회 2012 대한토목학회 학술대회 Vol.2012 No.10

HVPE법으로 성장시킨 GaN 단결정의 wet etching에 의한 표면 변화

오동근,최봉근,방신영,강석현,김소연,김새암,이성국,정진현,김경훈,심광보,Oh, Dong Keun,Choi, Bong Geun,Bang, Sin-Yeong,Kang, Suk Hyun,Kim, So Yeon,Kim, Sae Am,Lee, Seong Kuk,Chung, Jin Hyun,Kim, Kyoung Hun,Shim, Kwang Bo 한국결정성장학회 2012 한국결정성장학회지 Vol.22 No.6

본 연구에서는 HVPE법으로 사파이어 기판(0001) 위에 성장시킨 GaN epilayer의 etching에 따른 표면변화 특성을 조사하였다. 주사전자 현미경(SEM) 관찰 결과, 3가지 형태를 갖는 육각형 모양의 etch pit(edge, screw, mixed) 들이 GaN epilayer의 두께 변화에 따라서 형성되었다. 이러한 관통전위들은(TDs) epilayer의 두께가 얇고, etch pit density가 높을수록 screw and mixed type TDs이 많이 관찰되었고, 두께가 증가할수록 etch pit density가 낮아지면서 edge and mixed type TDs들이 주로 존재하는 것을 관찰 할 수 있었다. In this paper, we investigated characteristics of etching induced surface morphology variation by wet etching of GaN epilayer were grown on sapphire (0001) substrate by hydride vapor phase epitaxy (HVPE). As a results of scanning electron microscope (SEM) observation, three types of hexagonal etch pits (Edge, Screw, Mixed) were formed by the GaN epilayer thickness variations. A lot of etch pits, attributed to screw and mixed type TD, were observed at thinner epilayer, leading to high etch pit density. On the other hand, the thickness of GaN epilayer increased with the number of etch pits corresponding to edge and mixed dislocations, which are the majority of TDs are observed.

HVPE법으로 성장시킨 GaN substrate 제작과 특성 평가

오동근,최봉근,방신영,은종원,정준호,이성국,정진현,심광보,Oh, Dong-Keun,Choi, Bong-Geun,Bang, Sin-Young,Eun, Jong-Won,Chung, Jun-Ho,Lee, Seong-Kuk,Chung, Jin-Hyun,Shim, Kwang-Bo 한국결정성장학회 2010 한국결정성장학회지 Vol.20 No.4

본 연구에서는 HVPE을 이용하여 sapphire(001) 기판 위에 직경 2 inch, 두께 약 1.5 mm인 bulk GaN를 성장하고, 이를 mechanical polishing을 통해 $10{\times}10,\;15{\times}15$ mm 크기의 free-standing GaN template을 제작하여 그 특성을 평가하였다. 성장된 GaN 단결정의 X-ray diffraction pattern 결과 (002) 및 (004) 면으로부터의 회절에 의한 peak가 나타났으며, (002) 면의 DCXRD(Double crystal X-Ray diffraction) rocking curve peak의 반치폭(FWHM)은 98 arcsec으로 나타났다. 제작한 GaN template는 363 nm 파장에서 sharp한 PL spectrum을 나타내었으며, 불순물 defect에 의한 yellow 영역에서의 broad peak은 관찰되지 않았으며, 제작된 GaN template표면의 etch-pit 밀도는 $5{\times}10^6/cm^2$으로 매우 낮았다. 이러한 분석결과를 통하여 성장된 GaN template는 LED 및 LD 등의 청색 발광소자 및 고온, 고출력 소자용 기판재료로 응용이 가능할 것으로 생각 된다. Bulk GaN single crystal with 1.5 mm thickness was successfully grown by hydride vapor phase epitaxy (HVPE) technique. Free-standing GaN substrates of $10{\times}10,\;15{\times}15$ mm size were fabricate after lift-off of sapphire substrate and their optical properties were characterized properties for device applications. X-ray diffraction patterns showed (002) and (004) peak, and the FWHM of the X-ray rocking curve (XRC) measurement in (002) was 98 arcsec. A sharp photoluminescence spectrum at 363 nm was observed and defect spectrum at visible range was not detected. The hexagonal-shaped etch-pits are formed on the GaN surface in $200^{\circ}C\;H_3PO_4$ at 5 minutes. The defect density calculated from observed etch-pits on surface was around $5{\times}10^6/cm^2$. This indicates that the fabricated GaN substrates can be used for applications in the field of optodevice, and high power electronics.

이동위성 통신 시스템에서 억압 파일롯트 채널을 이용한 DS / CDMA의 성능 분석

정부영,최봉근,강영흥,이진,Chung, Boo-Young,Choi, Bong-Keun,Kang, Young-Heung,Lee, Jin 한국전자파학회 1997 한국전자파학회논문지 Vol.8 No.2

본 논문에서는 억압 파일롯트를 이용하여 복소 지연 프로파일을 추정, 코히어런트 Rake 다이버시티 합성을 실현하는 동시에 얻어진 지연 프로파일의 극대점을 찾아 칩동기를 행하는 DS /CDMA 방식의 성능평가를 이동위성 채널에서 해보았다. 이를 위해 shadowed Rician 페이딩 시뮬레이터를 구성하여 그 포락선 변동특성을 조사 하였고 이론적인 오율해석을 병행하였다. 그 결과로서 Heavy shadowing인 경우 그 포락선 변동은 지상이동 통신채널의 Rayleigh 페이딩의 완만한 주기적 변동에 비해 랜덤한 특성을 가져 심각한 데이터 오류를 가져 오리라 예상할 수 있다. 또한 이론적 오율해석으로부터 DS /CDMA방식은 협대역 QPSK 방식에 비해 Average shadowing하에서 약 10 dB이상 개선되었다. 그리고 억압 파일롯트 채널을 이용한 DS /CDMA 방식은 이동위성 채널에서 파일롯트 채널대 송선전력비, $\beta$=-8dB, 복소지연 프로파일수 $N_{profile}$=32 일때 오율성능변에서 최적점을 나타내며, 이값을 이용했을 때 Light shadowing하의 오율특성은 이상적인 QPSK 오율특성과 같은 결과를 얻을 수 있었다. In this paper, we have carried out the DS/CDMA with a suppressed pilot channel, which is used in receiving coherently with Rake diversity and in synchronizing the chip timing, in the mobile satellite communication. Also, we have investigated the envelope variation of a shadowed Rician fading simulator, and analyzed the error performences of DS/CDMA in the mobile satellite communication. The results showed that the error performance in the Heavy shadowing environment might be degraded more than in the Rayleigh fading environment since the fading envelopes in the former environment are varied randomly compared with those in the latter environment. And the performence of DS/CDMA system could be improved about 10 dB compared with that of narrowband QPSK system. In conclusion, DS/CDMA with a suppressed pilot channel had the best performance in the case of the suppressed pilot channel to transmission power ratio $\beta$=-8 dB, the number of complex delay profiles $N_{profile}$=32, and using these values, the error performance of DS/CDMA in Light shadowing environment was identical to the ideal QPSK error performance.

HVPE법으로 성장시킨 GaN 박막의 기판에 따른 극성 특성

오동근,최봉근,이성철,정진현,이성국,심광보,Oh, Dong-Keun,Lai, Van Thi Ha,Choi, Bong-Geun,Yi, Seong,Chung, Jin-Hyun,Lee, Seong-Kuk,Shim, Kwang-Bo 한국결정성장학회 2008 韓國結晶成長學會誌 Vol.18 No.3

HVPE 법에 의해 성장시킨 GaN 박막이 기판에 따라서 극성과 비극성 특성의 변화에 대해 연구하였다. A-plane($11{\bar{2}}0$), C-plane(0001) and M-Plane($10{\bar{1}}0$) 사파이어 기판을 이용하여 $10\;{\mu}m$ 두께의 GaN 박막을 성장하였다. 광학현미경 및 원자력간 현미경(OM, AFM)을 이용해 표면 구조를 관찰하고, HRXD를 통해 이들은 모두 wurtzite 구조를 갖고 C-plane으로 성장시에는, 극성 특성을, A-plane 및 M-plane 성장 시에는 비극성 특성을 가짐을 확인하였으며, Photoluminescence (PL)측정 결과 3.4 eV에서 발광 피크, 2.2 eV에서 yellow luminescence peak를 확인하였다. Polar and non-polar GaN was grown by the HVPE on various substrates and influence of polarity has been investigated. The $10\;{\mu}m$ thickness GaN were grown by HVPE is along A-plane ($11{\bar{2}}0$), C-plane (0001) and M-Plane ($10{\bar{1}}0$) sapphire substrate respectively. Surface properties were observed by optical microscope and atomic force microscopy. High resolution X-ray diffraction (HR-XRD) confirms the wurtzite structure. The donor band exciton peak located at ${\sim}3.4\;eV$ and also located yellow luminescence peak at 2.2 eV. The polarity of the GaN film has a strong influence on the morphology and the optical properties.

일개(一個) 종합병원(綜合病院) 건강검진자(健康檢診者)의 사상체질(四象體質)에 따른 만성병환(慢性病患)의 유병율(有病率)에 관(關)한 연구(硏究)

이태규,이수경,최봉근,송일병,Lee, Tae-Gyu,Lee, Soo-Kyung,Choi, Bong-Keun,Song, Il-Bing 사상체질의학회 2005 사상체질의학회지 Vol.17 No.2

1. Objectives The purpose of this study was to find out prevalence of chronic diseases according to Sasang constitutional. 2. Methods The medical records of 1,453 subjects who have taken health examinations and diagnosis of Sasang constitution from January 2003 to June 2003 at a health examination center of a university hospital in Seoul were reviewed. Sociodemographic factors and the prevalences of chronic diseases according to Sasang Constitution are compared and analyzed. 3. Results (1) Among the 1,453 subjects, 683(47.0%) were Taeumin, 421(29.0%) were Soyangin, and 349(24.0%) were Soeumin. (2) The prevalences of gastric polyp, diabetes mellitus, obesity, hypertension, hyperlipidemia, dyslipoproteinemia, abnormal liver function and fatty liver of T aeurnin were significantly higher than those of the other constitutions (p-value<0.05). And the prevalences of hepatic cyst and gall stone disease of Taeumin were higher than those of the other constitutions(p-value<0.l). (3) The prevalences of liver cirrhosis of Soyangin was significantly higher than that of the other constirutions(p-value <0. 05). (4) The prevalences of pulmonary tuberculosis on X-ray and anemia of Soeurnin were significantly higher than those of the other constitutions (p-value<0.05). And the prevalences of gastric xanthelasma and hypothyroidism of Soeumin were higher than those of the other constitutions(p-value<0.1). 4. Conclusions There were significant differences on the prevalences of some chronic diseases according to Sasang wnstirution.

촉매를 사용하지 않는 열 기화법으로 다양한 형태의 ZnO 3차원 구조체 합성

방신영,오동근,최봉근,함헌,김경훈,심광보,Bang, Sin Young,Tran, Van Khai,Oh, Dong Keun,Maneeratanasarn, Prachuporn,Choi, Bong Geun,Ham, Heon,Kim, Kyoung Hun,Shim, Kwang Bo 한국결정성장학회 2013 한국결정성장학회지 Vol.23 No.1

다른 형태의 ZnO는 형태에 따라 각각의 활용분야에 사용할 수 있다. 다양한 형태의 ZnO 구조체(structures)는 촉매를 사용하지 않는 열 기화법(thermal evaporation process)으로 합성되었다. ZnO 구조체의 형태들은 같은 실험 공정에서 기판과 소스간의 거리에 의존하였으며, 그 결과 합성물의 형태는 hollow, cage, star 이었다. ZnO 구조체의 형상과 결정성을 주사전자현미경(SEM)과 X선 회절분석(XRD)으로 각기 평가했다. 본 연구에서는 어떤 종류의 성장 요소가 최종 구조체의 형태에 관여하는지를 입증한다. ZnO with different morphologies can be used various application depending on their shapes. Different morphologies of ZnO structures were synthesized by a catalysis-free thermal evaporation process. Their morphologies were dependent on the distance from the source to substrate on the same processing condition; in the result were products morphologies of the hollow, cage and star. Their shapes and crystalinity were evaluated by SEM and XRD, respectively. This work demonstrates what kind of growth factors would be involved in the final structure morphologies.

우리나라 청소년의 신체활동과 사회경제적 변수와의 관련성

오인환,이고은,오창모,최경식,최봉근,최중명,윤태영,Oh, In-Hwan,Lee, Go-Eun,Oh, Chang-Mo,Choi, Kyung-Sik,Choe, Bong-Keun,Choi, Joong-Myung,Yoon, Tai-Young 대한예방의학회 2009 예방의학회지 Vol.42 No.5

Objectives : The physical activity of Korean adolescents and its distribution based on social characteristics have not yet been fully assessed. This study intends to reveal the distribution of physical activity by its subgroups and offer possible explanatory variables. Methods : The 3rd Korea Youth Risk Behavior Web-based Survey was analyzed for this study. The appropriateness of physical activity was defined by Korea s Health Plan 2010 and physical inactivity was assessed independently. Family affluence scale, parents education levels, subjective economic status, grade, and school location were considered explanatory variables. All statistical analysis was conducted using SAS ver. 9.1. Results : The proportion of participants engaging in vigorous physical activity was high in males (41.6%), at a low grade (38.5%), within the high family affluence scale group (35.5%). The distribution of participants engaging in moderate physical activity showed similar patterns, but the overall proportion was lower (9.8%). Low family affluence and students with lower subjective economic status reported a higher prevalence of physical inactivity. In multiple logistic regression analysis for physical activity, significant factors included family affluence scale (p<0.05). For physical inactivity, family affluence scale, parents education levels, and subjective economic status were included as significant factors (p<0.05). Conclusions : The results suggest that the physical activity and inactivity of adolescents may be affected by socioeconomic variables, such as family affluence scale. This implies the need to take proper measures to address these socio-economic inequalities.

AlN 단결정의 품질평가를 위한 molten KOH/NaOH eutectic alloy의 화학적 습식에칭

박철우,박재화,홍윤표,오동근,최봉근,이성국,심광보,Park, Cheol Woo,Park, Jae Hwa,Hong, Yoon Pyo,Oh, Dong Keun,Choi, Bong Geun,Lee, Seong Kuk,Shim, Kwang Bo 한국결정성장학회 2014 한국결정성장학회지 Vol.24 No.6

본 연구에서는 상용화되는 AlN 웨이퍼(wafer)를 이용하여 molten KOH/NaOH 화학적 습식 에칭(Wet Chemical Etching)에 따른 표면변화 특성 및 최적의 에칭 조건을 조사하였다. AlN 웨이퍼를 $350^{\circ}C$에서 5분간 에칭 시 Al-face, N-face는 서로 다른 관찰되었다. 특히, Al-face는 에치핏의 형상을 파악하여 결함특성을 관찰하였고, 이로부터 결함 밀도를 계산하여 $2{\times}10^6/cm^2{\sim}10^{10}/cm^2$의 결과를 얻었다. N-face의 경우 육각 뿔(hexagonal pyramids) 형태의 격자결함이 형성되었다. 또한 AlN 웨이퍼의 성장 시 배향을 관찰하기 위해 XRD(X-Ray Diffraction, Rigaku, JAPAN)를 이용하여 분석한 결과 육방정 AlN의 C축 방향에 해당되는 (0002) 및 (0004) 면으로 배향된 상태임을 알 수 있었고, DC-XRD(Double Crystal X-ray Diffraction, bruker, Germany)를 이용하여 rocking curve의 위치에 따라 곡률 반경을 측정했을 때 1.6~17 m의 곡률을 가지고 있는 것으로 나타났다. We investigated the optimal etching conditions and properties of the surface change due to molten KOH/NaOH chemical wet etching using an AlN wafer which has been put to practical use in the present study. Results were observed using a scanning electron microscope after 5 minutes etching at $350^{\circ}C$, was found to have a surface form of the respective other Al-face, the N-face. In particular, etch-pit in the form of a hexagon, which is observed in the Al-face appeared, It was calculated at $2{\times}10^6/cm^2{\sim}10^{10}/cm^2$ dislocation density. In the case of N-face, lattice defects in the form of the hexagonal pyramids is formed. It was discovered that in order to observe the orientation of the wafer, which corresponds to the C-axis direction of the resulting hexagonal AlN which was analyzed using XRD (0002) and is a state of being oriented in the (0004) plane. The Radius of curvature of AlN wafer was 1.6~17 m measured by DC-XRD rocking curve position.