• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.553-554
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• 2006

In this paper, 77 GHz CPW power amplifier MMIC, which are consisted of a 2 stage driver stage and a power stage employing $8{\times}50um$ gate width, have been successfully developed by using 120nm $In_{0.4}AlAs/In_{0.35}GaAs$ Metamorphic high electron mobility transistors (MHEMTs). The devices show an extrinsic transconductance $g_m$ of 660 mS/mm, a maximum drain current of 700 mA/mm, and a gate drain breakdown voltage of -8.5 V. A cut-off frequency ($f_T$) of 172 GHz and a maximum oscillation frequency ($f_{max}$) of over 300 GHz are achieved. The fabricated PA exhibited high power gain of 20dB only with 3 stages. The output power is measured to be 12.5 dBm.

• 한국방사선학회논문지
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• 제15권3호
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• pp.391-399
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• 2021

고상법을 이용하여 Eu 이온이 첨가된 다중인산염 NaSr(PO₃)₃형광체를 합성하고 탄소열환원법을 통하여 NaSr(PO₃)₃:Eu²⁺ 형광체를 완성하였다. X선 회절 측정(XRD)을 통하여 형광체의 결정상을 확인하였다. NaSr(PO₃)₃:Eu²⁺ 형광체의 Eu²⁺ 농도 변화에 따른 발광 방출 및 여기 스펙트럼과 수명시간을 측정하였다. 320 nm 근자외선 여기에서 NaSr(PO₃)₃:Eu²⁺ 형광체는 Eu²⁺의 4f⁶5d → f⁷(8S^7/2) 전이에 따른 420 nm 중심의 밴드를 방출하였다. Eu²⁺ 첨가 된 형광체의 열적 특성을 증가시키기 위해 온도 의존적 방출 스펙트럼과 형광 감쇠 곡선을 측정하고 형광체의 온도 의존성을 설명하였다. 본 연구로 희토류 이온이 첨가된 NaSr(PO₃)₃:Eu²⁺는 디스플레이, 검출기 등에 온도 센서 역할을 할 수 있는 우수한 온도 의존성을 보여준다.

• 한국전기전자재료학회논문지
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• 제23권7호
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• pp.545-549
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• 2010

Low-frequency noise (1/f noise) has been measured in order to analyze the Vth instability of ZnO TFTs having two different active layer thicknesses of 40 nm and 80 nm. Under electrical stress, it was found that the TFTs with the active layer thickness of 80 nm shows smaller threshold voltage shift (${\Delta}V_{th}$) than those with thickness of 40 nm. However the ${\Delta}V_{th}$ is completely relaxed after the removal of DC stress. In order to investigate the cause of this threshold voltage instability, we accomplished the 1/f noise measurement and found that ZnO TFTs exposed the mobility fluctuation properties, in which the noise level increases as the gate bias rises and the normalized drain current noise level($S_{ID}/{I_D}^2$) of the active layer of thickness 80 nm is smaller than that of active layer thickness of thickness 40 nm. This result means that the 80 nm thickness TFTs have a smaller density of traps. This result correlated with the physical characteristics analysis performmed using XRD, which indicated that the grain size increases when the active layer thickness is made thicker. Consequently, the number of preexisting traps in the device increases with decreasing thickness of the active layer and are related closely to the $V_{th}$ instability under electrical stress.

• Journal of Ceramic Processing Research
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• 제20권2호
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• pp.158-163
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• 2019

Er3+/Yb3+-codoped NaLa(MoO4)2 colloidal nanocrystals were synthesized by pulsed laser ablations in de-ionized water and sodium dodecyl sulfate (NaC12H25SO4, SDS) aqueous solution for up-conversion (UC) luminescence bio-labeling applications. The influences of the SDS molecules on the crystallinities, crystal morphologies, crystallite sizes, and UC luminescence properties of the prepared Er3+/Yb3+-codoped NaLa(MoO4)2 colloidal nanocrystals were investigated in detail. Under a 980-nm excitation, the Er3+/Yb3+-codoped nanocolloidal NaLa(MoO4)2 suspension exhibited a weak red emission near 670 nm and strong green UC emissions at 530 and 550 nm, corresponding to the intra 4f transitions of Er3+ (4F9/2, 2H11/2, 4S3/2) → Er3+ (4I15/2). When the SDS solution was used, a smaller average crystallite size, narrower size distribution, and enhanced UC luminescence were observed. These characteristics were attributed to the amphoteric SDS molecules attached to the positively charged Er3+/Yb3+-codoped NaLa(MoO4)2 colloidal nanocrystals, effectively occupying the oxygen defect on their surfaces. The Er3+/Yb3+-codoped nanocrystalline NaLa(MoO4)2 suspension prepared in the SDS solution exhibited a remarkably strong green emission visible to the naked eyes.

• 전자공학회논문지D
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• 제35D권5호
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• pp.33-39
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• 1998

The BST (Ba$_{1-x}$ Sr$_{x}$TiO$_{3}$)(50/50) thin film has been grown by RF magnetron reactive sputtering and its characteristics such as crystallization, surface roughness, and electrical properties have been investigated with varying the film thickness. The crystallization and surface roughness of BST thin film are investigated by using XRD and AFM, respectively The BST thin film anealed at 800.deg. C for 2 min has pure perovskite structure and good surface roughness of 16.1.angs.. We estimate that the thickness and dielectric constant of interface layer between BST film and electrode are 3nm and 18.9, respectively, by measuring the capacitance with various film thickness. As the film thickness increases form 80nm to 240nm, the dielectric constant at 10kHz increases from 199 to 265 and the leakage current density at 200kV/cm decreases from 0.682.mu.A/cm$^{2}$ to 0.181 .mu.A/cm$^{2}$. In the case of 240nm-thick BST thin film, the charge storage density and leakage current density at 5V are 50.5fC/.mu.m$^{2}$ and 0.182.mu.A/cm$^{2}$, respectively. The values indicate that the BST thin film is a very useful dielectric material for the DRAM capacitor.or.

• 한국결정성장학회지
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• 제13권5호
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• pp.205-210
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• 2003

스컬법에 의해 alexandrite-like cubic zirconia 단결정을 성장 시켰다. 스컬용융시 R.F generator는 35 ㎾, 2 MHz 였다. 단결정들은 전이금속이온인 Pr을 1 또는 1.5 wt%와 Nd를 0.5 또는 l wt%를 함께 첨가하여 성장시켰으며, 성장 후0.25 mm의 slice와 12 mm의 round brilliant cut으로 연마하였다. 연마석은 공기중 또는 질소분위기에서 $1000^{\circ}C$에서 2시간 열처리하였으며 optical absorption spectra($\lambda$ = 400∼700 nm)를 얻었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.57-58
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• 2008

We have studied an organic layer and semitransparent Al electrode thickness dependent optical properties and microcavity effects for top-emission organic light-emitting diodes. Manufactured top-emission device structure is Al(100nm)/TPD(xnm)/Alq(ynm)/LiF(0.5nm)/Al(25nm). While a thickness of total organic layer was varied from 85nm to 165n, a ratio of those two layers was kept to be about 2:3. Semitransparent Al cathode was varied from 20nm to 30nm for the device with an organic layer total thickness of 140nm. As the thickness of total organic layer increases, the emission spectra show a shift of peak wavelength from 490nm to 580nm, and the full width at half maxima from 90nm to 35nm. The emission spectra show a blue shift as the view angle increases. Emission spectra depending on a transmittance of semitransparent cathode show a shift of peak wavelength from 515nm to 593nm. At this time, the full width at half maximum was about to be a constant of 50nm. With this kind of microcavity effect, we were able to control the emission spectra from the top-emission organic light-emitting diodes.

• Journal of the Optical Society of Korea
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• 제20권6호
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• pp.778-783
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• 2016

We synthesized $Er^{3+}-Yb^{3+}$, $Pr^{3+}-Yb^{3+}$, and $Er^{3+}-Pr^{3+}-Yb^{3+}$ -doped oxyfluoride glass ceramics containing $CaF_2$ nanocrystals by proper thermal treatments. Spectral characteristics of down- and up-converted emissions in three kinds of glass ceramics under 365-nm and 980-nm excitations were compared and explained by cross relaxations, excited-state absorptions, and energy-transfer processes between different ions. The huge reduction of up-conversion emission in the triply doped glass ceramics under 980-nm excitation compared to the $Er^{3+}-Yb^{3+}$ codoped one was explained by the split pump power and the direct energy transfer from $Er^{3+}$ to $Pr^{3+}$ ions. Increasing $Yb^{3+}$ concentration from 2% to 10% in the triply doped glass ceramics showed more than quadratic enhancement of the absorbed power, and we explained it by the enhanced energy-transfer efficiency from $Yb^{3+}$ to $Er^{3+}$ ions. We also observed enhanced up-converted emissions of $Er^{3+}$ and $Pr^{3+}$ ions in three kinds of glass ceramics under simultaneous excitation at 980 nm and 1550 nm, and suggested detailed up-conversion mechanisms.

• Journal of Astronomy and Space Sciences
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• 제24권4호
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• pp.297-308
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• 2007

2010년에 발사될 예정인 아리랑위성 5호의 부 탑재체인 AOPOD(Atmosphere Occultation and Precision Orbit Determination) 시스템은 GPS(Global Positioning System) 전파 엄폐(radio occultation) 자료를 제공한다. 이 논문에서는 아리랑위성 5호 궤도에서 발생하는 GPS 전파 엄폐의 발생 빈도 및 분포를 시뮬레이션하고, 현재 천문연구원에서 개발 중인 GPS 전파 엄폐 자료처리시스템인 KROPS(KASI Radio Occultation Processing System)를 사용한 전리층 전자밀도 산출결과를 제시하였다. 전자밀도를 산출하기 위해 2004년 6월 20일에 발생한 CHAMP(CHAllenging Minisatellite Payload) 위성의 GPS 전파 엄폐 관측값을 사용하였고 산출된 결과는 IRI(International Reference Ionosphere) - 2001 모델과 CHAMP 위성의 랑뮈어 탐침기(Planar Langmuir Probe) 및 이온존데 간과 비교하였다. 산출된 전자밀도를 이온존데 값과 비교했을 때, $F_2$층 최대전자밀도 고도인 $hmF_2$에서 약 5km, $F_2$층 최대전자밀도인 $NmF_2$에서 약 $3{\times}10^{10}el/m^3$의 차이를 보였으며, 랑뮈어 탐침기 값과 비교하여 고도 365.6km에서 두 값 모두 $1.6{\times}10^{11}el/m^3$로 일치하였다.

• 한국인터넷방송통신학회논문지
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• 제23권1호
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• pp.157-162
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• 2023

본 논문은 NP-완전으로 알려진 3-SAT 문제에 대해 O(nm)의 다항시간 알고리즘을 제안하였다. 여기서 n은 3-SAT 수식 f에 포함된 문자수이며, m은 모든 문자의 총 발생 빈도수이다. 제안된 알고리즘은 우선순위롤 정하여 문자의 진리 값을 결정하였다. 하나의 절에 포함된 최소 문자의 수가 1개(k=1)인 문자, k≥2 이고 진리 값이 '0' 또는 '1'만 존재하는 문자, 발생 빈도수가 최소인 문자 우선순위로 진리 값을 결정하였다. 진리 값이 결정된 문자의 r인 절을 삭제하고, 남아 있는 절에서 해당 문자를 삭제하는 방법으로 식을 축소시킨다. 이 과정을 문자 수 l회를 수행하면 주어진 f의 충족 가능 여부를 결정할 수 있다. 이 방법을 적용한 결과 주어진 식 f의 충족 가능 여부를 판단할 수 있었으며, 모든 문자의 진리 값도 결정할 수 있었다. 제안된 알고리즘을 다양한 문제들에 적용한 결과 모든 문제들에서 충족가능 여부를 정확히 결정할 수 있었다. 결국, 제안된 알고리즘은 모든 SAT 문제를 선형시간으로 풀 수 있는 일반화된 알고리즘으로 확장 가능하며, 오랜 숙원이던 P vs. NP 문제를 풀 수 있는 기반을 제공하였다.