• Transactions on Electrical and Electronic Materials
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• 제15권6호
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• pp.320-323
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• 2014

Ga-doped $LiFePO_4$ cathode materials were synthesized using a hydrothermal method. The microstructural characteristics and electrochemical performances were systematically investigated using field emission scanning electron microscopy, high-resolution X-ray diffraction, energy dispersive X-ray spectroscopy, charge-discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. Among the as-prepared samples, $LiFe_{0.96}Ga_{0.04}PO_4$ demonstrates the best electrochemical properties in terms of discharge capacity, electrochemical reversibility, and cycling performance with an initial discharge capacity of $125mAh\;g^{-1}$ and high lithium ion diffusion coefficient of $1.38{\times}10^{-14}cm^2s^{-1}$ (whereas for $LiFePO_4$, these were $113mAh\;g^{-1}$ and $8.09{\times}10^{-15}cm^2\;s^{-1}$, respectively). The improved electrochemical performance can be attributed to the facilitation of Li+ ion effective diffusion induced by $Ga^{3+}$ substitution.

• 한국전기전자재료학회논문지
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• 제30권5호
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• pp.270-275
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• 2017

Current progress in the development of semiconductor technology in applications involving high electron mobility transistors (HEMT) and power devices is hindered by the lack of adequate ways todissipate heat generated during device operation. Concurrently, electronic devices that use gallium nitride (GaN) substrates do not perform well, because of the poor heat dissipation of the substrate. Suggested alternatives for overcoming these limitations include integration of high thermal conductivity material like diamond near the active device areas. This study will address a critical development in the art of GaN on diamond (GOD) structure by designing for ideal heat dissipation, in order to create apathway with the least thermal resistance and to improve the overall ease of integrating diamond heat spreaders into future electronic devices. This research has been carried out by means of heat transfer simulation, which has been successfully demonstrated by a finite-element method.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2010년도 추계학술발표논문집 1부
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• pp.76-79
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• 2010

본 논문에서는 고 효율 및 고 출력 특성을 가지는 질화갈륨(GaN) 소자를 이용하여 WiMAX 및 LTE System에 사용될 수 있는 DPD용 Pallet Amplifier를 제작하였다. 제작된 Pallet Amplifier는 Pre-drive로써 저 전류의 MMIC를 채택하고, Drive 단과 Main 단에 15W 급과 30W 급의 질화갈륨 소자를 사용 하였으며, 추가적인 효율 개선을 위해 PCB상에 Doherty Structure를 적용함으로써 보다 높은 효율을 구현하였다. 제작된 Pallet Amplifier는 음 전원 Bias 제어 회로, 온도에 따른 Gain 보상회로, Sequence 회로 및 Main 전원 Drop에 따른 보호 회로를 구현하였다. WiMAX Signal을 이용한 Modulation Power 10Watt Test에서 약 36.8~38.3%의 Pallet 효율과 DPD Solution인 TI GC5325SEK DPD Board 사용 시 ACLR은 약 46dBc 이상을 가지는 것으로 측정되었다. 본 논문에서 제작된 Pallet Amplifier는 Upper Band와 Lower Band로 나누어 제작되었던 기존 Pallet Amplifier와 달리 하나의 Pallet Amplifier로 2496~2690MHz에서 모두 사용하면서 종전에 사용되고 있는 Pallet Amplifier에 비해 Size가 최소 10% 이상 축소되어 효율 및 크기 면에서 종전 Pallet Amplifier보다 큰 이점을 갖는다.

• Transactions on Electrical and Electronic Materials
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• 제15권2호
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• pp.66-68
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• 2014

Most commercial white LED lamps use blue chip coated with yellow emitting phosphor. The use of blue excitable red and green phosphors is expected to improve the CRI. Several phosphors, such as $SrGa_2S_4:Eu^{2+}$ and $(Sr,Ba)SiO_4:Eu^{2+}$, have been suggested in the past as green components. However, there are issues of the sensitivity and stability of such phosphors. Here, we describe gallium substituted $YAG:Ce^{3+}$ phosphor, as a green emitter. YAG structures are already accepted by the industry, for their stability and efficiency. LEDs with improved CRI could be fabricated by choosing $Y_3Al_4GaO_{12}:Ce^{3+}$ (green and yellow), and $SrS:Eu^{2+}$ (red) phosphors, along with blue chip. Also, the effect of a slight change in chip wavelength is studied, for two phosphor-coated w-LEDs. The reduction in particle size of the coated phosphors also gives improved w-LED characteristics.

• Journal of Chest Surgery
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• 제27권10호
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• pp.850-853
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• 1994

Open lung biopsy was performed in thirty patients for the diagnosis and staging evaluation of interstitial lung disease during the period from January 1987 until December 1992. The age of the patients ranged from 14 to 71 years [mean 48 years], and the patients consisted of 14 males and 16 females. Preoperative FEV1`s were from 0.80 liter to 3.88 liters [mean 1.66]. Other non-invasive diagnostic studies such as PCNA, bronchoalveolar lavage, TBLB, and gallium scan were also done in addition to X-ray and high-resolution chest CT. Tweaty-eight were correctly diagnosed and 2 cases were not [diagnostic yield rate 93.3%]. Among the 28 cases,pathologic diagnosis influenced further treatment regimens and prognostic expectations in 23 cases [82.1%]. The diagnostic non-invasive studies other than open lung biopsy yielded a correct diagnosis without staging only in 5 cases. There was no mortality and only one complication, ARDS ; however, the patient recovered after 5 days ventilator support. Open lung biopsy, which is the gold standard for the diagnosis and staging evaluation of interstitial lung disease can be done safely and has value in clinical decision making. Also knowledge of the involvement of the lesion is important for proper selection of the biopsy site.

• 한국분말재료학회지
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• 제21권5호
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• pp.338-342
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• 2014

In the present work, we investigated the mechanical alloying of binary Ga-Se(1:1) and Ga-Te(1;1) sysyems. The high-energy ball-milling was performed at $40^{\circ}C$ where one of constituents (Ga) is molten state. The purpose of the work was to see whether reactions between constituent elements are accelerated by the presence of a liquid phase. During the ball-milling, the liquid Ga phase completely disappeared and the resulting powders consist of nanocrystalline grain of ~20 nm with partly amorphized phases. However, no intermetallic compounds formed in spite of the presence of the liquid phases which has much higher diffusivity than solid constituents. By subsequent heat-treatments, the intermetallic compounds such as GaSe and GaTe formed at relatively low temperatures. The formation temperature of theses compound was much lower than those predicted by equilibrium phase diagram. The comparison of the ball-milled powders with un-milled ones indicated that the easy formation of intermetallic compound or allying occurs at low temperatures.

• 한국표면공학회지
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• 제36권2호
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• pp.135-140
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• 2003

The difference in lattice parameter and thermal expansion coefficient between GaN and Si which results in many defects into the grown GaN is larger than that between GaN and sapphire. In order to obtain high quality GaN films on Si substrate, it is essential to understand growth characteristics of GaN. In this study, GaN layers were grown on Si(111) substrates by MOCVD at three different GaN growth temperatures ($900^{\circ}C$, $1,000^{\circ}C$ and $1,100^{\circ}C$), using AlN and LT-GaN buffer layers. Using TEM, we carried out the comparative investigation of growth characteristics of GaN by characterizing lattice coherency, crystallinity, orientation relationship and defects formed (transition region, stacking fault, dislocation, etc). The localized region with high defect density was formed due to the lattice mismatch between AlN buffer layer and GaN. As the growth temperature of GaN increases, the defect density and surface roughness of GaN are decreased. In the case of GaN grown at $1,100^{\circ}$, growth thickness is decreased, and columns with out-plane misorientation are formed.

• 전자통신동향분석
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• 제29권6호
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• pp.53-62
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• 2014

본고는 최근 화두가 되고 있는 에너지 절감을 위해 고효율, 친환경의 WBG(Wide Band-Gap) 화합물반도체인 SiC(Silicon Carbide), GaN(Gallium Nitride) 전력반도체 소자 및 전력변환 모듈의 기술동향과 ETRI에서 연구개발 진행 중인 GaN 전력반도체 관련 기술에 대해 기술한다. WBG 전력반도체는 기존의 실리콘 전력반도체와 비교하여 열 특성 향상, 고속 스위칭, 고전압/고전류 특성 및 스위칭 손실 최소화 등이 가능하고 이에 따른 시스템의 소형화 및 전력효율 향상 효과를 얻을 수 있다. 특히, GaN 전력반도체 소자는 시장이 가장 넓게 형성되어 있는 900V 이하에 적용이 가능하며, 앞으로 시장이 커질 것으로 예상되는 HEV(Hybrid Electric Vehicle)/EV(Electric Vehicle)의 친환경 자동차에도 활용될 것으로 기대되고 있다. 본고는 최근의 일본과 미국에서의 WBG 전력반도체에 대한 관심 및 투자 방향과 GaN 전력반도체 소자에 대한 해외 기업의 업계동향에 대해서도 함께 살펴본다. 이러한 WBG 전력반도체에 대한 해외 선진업체의 산업동향과 더불어 ETRI에서 연구개발 중인 GaN 전력반도체 기술현황에 대해 전력소자 설계 및 제조공정, 패키징, 전력모듈 설계 제작 기술을 포함하여 기술한다.

• Journal of Information Display
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• 제11권4호
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• pp.165-168
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• 2010

A solution-processed multicomponent oxide, yttrium hafnium zinc oxide (YHZO), was synthesized and deposited as a gate insulator. The YHZO film annealed at $600^{\circ}C$ contained an amorphous phase based on the results of thermogravimetry, differential thermal analysis, and X-ray diffraction. The electrical characteristics of the YHZO film were analyzed by measuring the leakage current. The high dielectric constant (16.4) and high breakdown voltage (71.6 V) of the YHZO films resulted from the characteristics of $HfO_2$ and $Y_2O_3$, respectively. To examine if YHZO can be applied to thin-film transistors (TFTs), indium gallium zinc oxide TFTs with a YHZO gate insulator were also fabricated. The desirable characteristics of the YHZO films when used as a gate insulator show that the limitations of the general binary-oxide-based materials and of the conventional vacuum processes can be overcome.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.1097-1100
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• 2008

We demonstrate that the performance of amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFT) can be optimized by controlling the interfaces between IGZO and sandwiching insulators and by proper deposition of IGZO layer. Specifically, contact and channel resistances are decreased by reducing IGZO bulk resistance and optimizing dry-etch process, respectively. Field-effect mobility ($\mu_{FE}$) and subthreshold gate swing (S) are further enhanced by fine-tuning IGZO deposition condition.