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장호정(Ho Jung Chang),손창식(Chang-Sik Son),허재성(Jae Sung Hur) 한국표면공학회 2007 한국표면공학회지 Vol.40 No.2
We have investigated the optical and electrical properties of surface mounted white light emitting diode (LED) chips prepared by using yellow phosphors on the blue LED chip. The yellow phosphor mixed with transparent epoxy was coated on the prepared LED chip. The optimum mixing conditions with epoxy and yellow phosphor is obtained at the mixing ratio of epoxy:yellow phosphor = 97:3 wt%. The maximum luminance and light emitting efficiency are above 80,000 cd/㎡ and 23.2 ㏐/W, respectively, at the bias voltage of 2.9 V. There was no distinct change in the luminance strength with changing of the yellow phosphor ratios. The current of the white LED chip is about 30 mA at 2.9 V.
ITO/Glass 기판위에 PFO-poss 유기 발광층을 가지는 고분자 발광다이오드의 제작
유재혁,장호정,Yoo, Jae-Hyouk,Chang, Ho-Jung 한국마이크로전자및패키징학회 2006 마이크로전자 및 패키징학회지 Vol.13 No.4
ITO(Indium tin oxide)glass 기판 위에 PEDOT:PSS[poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate)]와 PVX[poly(N-vinyl carbazole)] 고분자 물질을 정공 주입 및 수송층으로, 발광층으로 PFO-poss[Poly(9,9-dioctylfluorenyl-2,7-diyl) end capped with poss]를 사용하여 ITO/PEDOT:PSS/PVK/PFO-poss/LiF/Al 구조의 고분자 발광다이오드를 제작하였다. 이때 스핀코팅을 위한 발광 유기재료의 농도와 열처리 온도가 소자의 전기적, 광학적 특성에 미치는 영향을 조사하였다. 동일한 PFO-poss 농도에서 열처리 온도가 $100^{\circ}C$에서 $200^{\circ}C$로 증가할 경우 PLED 소자의 전류밀도와 휘도특성이 증가하는 경향을 나타내었다. 1.0 wt% 농도를 갖는 PFO-poss 유기물 발광충을 $200^{\circ}C$ 온도로 열처리 할 경우 $958\;cd/m^{2}$의 최대 휘도를 나타내었으며 발광파장은 523 nm 녹색계통의 파장이 크게 증가하여 청백색에 가까운 발광을 나타내었다. PFO-poss 농도증가(0.5 wt%에서 1.0 wt%)와 함께 PLED 소자의 열처리 온도를 $100^{\circ}C$에서 $200^{\circ}C$로 증가할 경우 CIE 색좌표는 청색 (x, y : 0.17, 0.14)에서 청백색 (x, y = 0.29, 0.41)발광으로 천이하는 경향을 나타내었다. Polymer light emitting diodes (PLEDs) with ITO/EDOT:PSS/PVK/PFO-poss/LiF/Al structures were prepared by the spin coating method on ITO(indium tin oxide)/glass substrates. PFO-poss[Poly(9,9-dioctylfluorenyl-2,7-diyl) end capped with poss] was used as light emitting polymer. PVK[poly(N-vinyl carbazole)] and PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)] polymers were used as the hole injection and transport materials. The effect of PFO-poss concentration and the heating temperatures on the electrical and optical properties of the devices were investigated. At the same concentration of PFO-poss solution, the current density and luminance of PLED device tend to increase as the annealing temperature increase from $100^{\circ}C$ to $200^{\circ}C$. The maximum luminance was found to be about 958 cd/m2 at 13V for the PLED device with 1.0 wt% PFO-poss at the annealing temperature of $200^{\circ}C$. In addition, the PLED device showed bluish white emission through the strong greenish peak with 523 nm in wavelength. As the concentration of PFO-poss increase from 0.5 wt% to 1.0 wt% and temperature of PLEDs increase from $100^{\circ}C$ to $200^{\circ}C$, the emission color tend to be shifted from blue with (x, y) = (0.17,0.14) to bluish white with (x, y) : (0.29,0.41) in CIE color coordinate.
ITO/PEDOT:PSS/MEH-PPV/Al 구조의 고분자 유기발광다이오드의 특성 연구
공수철,장호정,Gong, Su-Cheol,Chang, Ho-Jung 한국마이크로전자및패키징학회 2005 마이크로전자 및 패키징학회지 Vol.12 No.3
ITO(indium tin oxide)/Glass 기판위에 정공 수송층으로 PEDOT:PSS[poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)]과 발광층으로 MEH-PPV[poly(2-methoxy-5-(2-ethyhexoxy)-1,4phenylenvinylene)]의 고분자를 사용하여 ITO/PEDOT:PSS/MEH-PPV/Al 구조를 갖는 고분자 유기 발광다이오드 (polymer light emitting diode: PLED)를 제작하였다. 고분자 유기 발광다이오드 제작시 MEH-PPV의 농도$(0.1\;wt\%\~0.9\;wt\%)$가 발광층 표면 거칠기와 박막층판의 마찰계수(friction coefficient)에 미치는 영향을 조사하였다. MEH-PPV의 농도를 $0.1\;wt\%$에서 $0.9\;wt\%$로 증가함에 따라 발광층의 RMS 값은 1.72 nm 에서 1.00 nm로 감소하여 거칠기가 개선되는 경향을 보여 주었다. 또한 발광층 박막의 마찰계수는 0.048에서 0.035로 감소하여 박막의 접합상태가 나빠지는 현상을 나타내었다. $0.5\;wt\%$의 농도를 갖는 PLED 다이오드에서 최대 휘도인 $409\;cd/m^2$ 값을 얻었다. The polymer light emitting diodes (PLED) with ITO/PEDOT:PSS/MEH-PPV/Al structure were prepared on ITO(indium tin oxide)/Glass substrates using PEDOT:PSS[poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)] as the hole transport material and MEH-PPV[poly(2-methoxy-5-(2-ethyhexoxy)-1,4phenylenvinylene)] as emission material layer. The dependences on the surface roughnees and friction coefficient between film layers were investigated as a function of the MEH-PPV concentrations$(0.1\;wt\%\~0.9\;wt\%)$. The RMS values decreased from 1.72 nm to 1.00 nm as the concentration of MEH-PPV increased from $0.1\;wt\%\;to\;0.9\;wt\%$, indicating improvement of surface roughness. In addition, friction coefficients decreased from 0.048 to 0.035, which means the deteriorating of the adhesion condition. The PLED sample with $0.5\;wt\%$ of MEH-PPV showed the maximum luminance of $409\;cd/m^2$.
정공 주입층 및 수송층에 따른 고분자 유기발광다이오드의 특성 연구
신상배,장호정,Shin, Sang-Baie,Chang, Ho-Jung 한국마이크로전자및패키징학회 2007 마이크로전자 및 패키징학회지 Vol.14 No.4
본 연구에서는 ITO/PEDOT:PSS/PFO:MEH-PPV/LiF/Al의 구조를 갖는 고분자 유기발광다이오드를 제작하여 정공 주입층으로 사용되는 PEDOT:PSS의 두께 변화와 PVK 정공 수송층을 도입하여 ITO/PEDOT:PSS/PVK/PFO:MEH-PPV/LiF/Al 구조를 갖는 고분자 유기발광 다이오드를 제작하여 정공수송층이 유기발광다이오드의 전기 광학적 특성에 미치는 영향에 대하여 조사, 비교하였다. 실험에 사용된 모든 유기물은 플라즈마 처리된 ITO/glass 기판위에 스핀 코팅법으로 도포하였다. 정공 주입층인 PEDOT:PSS 두께를 약 80 nm에서 50 nm로 감소한 경우 PLED 소자의 휘도는 약 $220cd/m^2$ 에서 $450cd/m^2$으로 크게 증가하였다. 이러한 결과는 정공 주입층의 두께가 감소할수록 ITO 전극에서 발생한 정공이 보다 쉽게 발광막으로 전달되기 때문이다. 또한 PVK 정공 수송층을 도입한 PLED소자에서 최대 전류밀도와 휘도는 $268mA/cm^2$ 와 $540cd/m^2$ (at 12V)의 값을 각각 나타내었다. PVK 정공 수송층이 도입되지 않은 소자에 비해 전류밀도는 약 14%, 휘도는 약 22%의 특성개선을 나타내었다. We fabricated the polymer light emitting diodes (PLEDs) with ITO/PEDOT:PSS/PVK/PFO:MEH-PPV/LiF/Al structures. The effect of the thickness of PEDOT:PSS hole injection layer(HIL) on the electrical and optical properties of PLEDs was investigated. In addition, PVK hole transport layer(HTL) was introduced in the PLED device, and compared the properties of the PLEDS with and without PVX layer. All organic film layers were prepared by the spin coating method on the plasma treated ITO/glass substrates. As the thickness of PEDOT:PSS film layer decreased from about 80 nm to 50 nm, the luminance of PLED device increased from $220cd/m^2$에서 $450cd/m^2$. This may be ascribed to the increased transportation efficiency of the holes into the emission layer of PLED. The maximum current density and luminance were obtained fir the PLED device with PVX hole transport layer, showing that the current density and luminance were $268mA/cm^2\;and\;540cd/m^2$ at 12V, respectively. This values were improved by about 14% and 22% in current density and luminance compared with the PLED device without PVK layer.
졸-겔법으로 Pt/Ti/SiO<sub>2</sub>/Si 기판위에 제작된 (Bi,La)Ti<sub>3</sub>O<sub>12</sub> 강유전체 박막의 특성 연구
황선환,장호정,Hwang, Sun-Hwan,Chang, Ho-Jung 한국재료학회 2002 한국재료학회지 Vol.12 No.11
Metal-Ferroelectric-Metal(MFM) capacitors were prepared using $Bi_{3.3}$ $La_{0.7}$ $Ti_3$$O_{12}$ (BLT) ferroelectric thin films which were spin coated on $Pt/Ti/SiO_2$/Si substrates by the Sol-Gel method. BLT thin films annealed at above $650^{\circ}C$ showed polycrystalline structures with typical c-axis preferred orientation. The grain size and surface roughness were increased as the annealing temperature increased from $650^{\circ}C$ to $700^{\circ}C$. In addition, the full width at half maximum (FWHM) values were decreased with increasing annealing temperatures, indicating the improvement of crystallinity. The remanent polarization (2Pr= $Pr^{+}$ $+Pr^{-) }$ and leakage current of the BLT film annealed at $650^{\circ}C$ were about 29.3 $\mu$C/cm$^2$ and $2.3$\times$10^{-8}$$ A/cm^2$ at 3V. There were no distinct changes in the retention charges after $10^{10}$ polarization switching cycles, showing good fatigue property of the annealed BLT films.