• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.11
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• pp.1081-1090
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• 2013

In this paper, a C-band 10 W power amplifier with internally matched input and output matching circuit is designed and fabricated. The used power transistor for the power amplifier is GaAs pHEMT bare-chip. The wire bonding analysis considering the size of the capacitor and the position of transistor pad improves the accurate design. The matching circuit design with the package effect using EM simulation is performed. To reduce the unsymmetry of IMD3 in 2-tone measurement due to the memory effect, the bias circuit minimizing the memory effect is proposed and employed. The measured $P_{1dB}$, power gain, and power added efficiency are 39.8~40.4 dBm, 9.7~10.4 dB, and 33.4~38.0 %, respectively. Adopting the proposed bias circuit, the difference between the upper and lower IMD3 is less than 0.76 dB.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.5
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• pp.40-47
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• 1998

This paper report sthe design, fabrication and characterization of an AlGaAs/GaAs HBT (heterojunction bipolar transistor) with an air-bridge isolation structure which is made to improve high frequency characteristics for the application to the mobile communication system in the next genration. We found that the size, shape and structure of HBT have an effect on the high frequency operation. The measured dc and ac characteristics of the four type HBTs were compared and analyzed. An E-type HBT with an air-bridge structure by undercut etching exhibited .beta.=56, $V_{off-set}$ = 0.3 V, B $V_{CEO}$=7.0V with $f_{T}$=40 GHz and $f_{max}$=45GHz at a collector current density of 7.1*10$^{4}$ A/c $m^{2}$.>.

• Journal of electromagnetic engineering and science
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• v.7 no.2
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• pp.64-68
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• 2007

An InGaP/GaAs HBT based differential Colpitts voltage control oscillator(VCO) is presented in this paper. In the VCO core, two switching transistors are introduced to steer the core bias current to save power. An LC tank with an inductor quality factor(Q) of 11.4 is used to generate oscillation frequency. It has a superior phase noise characteristics of -130.12 dBc/Hz and -105.3 at 1 MHz and 100 kHz frequency offsets respectively from the carrier frequency(1.566 GHz) when supplied with a control voltage of 0 volt. It dissipates output power of -5.3 dBm. Two pairs of on-chip base collector (BC) diodes are used in the tank circuit to increase the VCO tuning range(168 MHz). This VCO occupies the area of $1.070{\times}0.90mm^2$ including buffer and pads.

• Journal of the Korean Ceramic Society
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• v.35 no.11
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• pp.1148-1154
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• 1998

Ga K-edge EXAFS spectra of PbO-Ga2O3 glasses were recorded at liquid nitrogen temperature and analyz-ed in order to quantitatively understand the medium-range-order arrangement around gallium in the glasses. The second peak was generated from a backscattering of the neighbor balliums and the Ga-Ga distance is ~3.13 A with Ga coordination number of ~2.7 Therefore GaO4 tetrahedra are connected through the cor-ner~sharing mode and form their own clusters made of the tetrahedra sharing more than 3 corners while some chains or rings are also present. These connection schemes of the GaO4 tetrahedra are believed to form the substantial part of the network structure.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.4
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• pp.33-37
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• 1992

AlGaAs/GaAs quantum well delta-doped channel FET's have been successfully fabricated using by low-pressure metalorganic chemical vapor deposition(LP-MOCVD). The FET's with a gate dimension of 1.8$\mu$m $\times$ 100$\mu$m have a maximum transconductance of 190 mS/mm and a maximum current density of 425 mA/nm. The devices show extremely broad transconductances with a large voltage swing of 2.4V. The S-parameter measurements have indicated that the current gain and power gain cutoff frequencies of the device were 7 and 15 GHz, respectively. These values are among the best performance reported for GaAs based heterojunction FET's with a similar device geometry.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.13-14
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• 2002

우물두께가 각각 1.5, 3.0, 4.5, 6.0 nm이고 장벽두께가 7.5 nm로 일정한 10 주기의 In0.15Ga0.8SN/GaN 다중 양자우물 구조(MQW)의 구조적 특성변화를 HRXRD(high resolution X-ray diffraction)를 이용하여 조사하였다. 구조적 특성변화를 살펴보기 위해 GaN (0002) 회절면의 ω/2θ-scan과 ω-scan 그리고 GaN (10-15) 역격자점 주위의 산란강도 분포도를 측정하였다. 우물두께가 증가할수록 시료의 평균변형률이 증가하였고, 우물두께가 1.5, 3.0, 4.5 nm인 MQW는 GaN 에피층과 격자정합을 이루며 성장된 반면 6.0 nm인 시료에서는 격자이완이 나타나 결정성이 저하된 것을 확인할 수 있었다. (그림 1) 따라서 본 연구에서 사용한 시료에서 6.0 nm의 우물두께가 격자이완의 임계두께임을 알 수 있었다. PL(photoluminescence) 스펙트럼 결과를 통하여 6.0 nm 우물두께의 시료가 다른 시료에 비하여 상대발광강도가 낮아지는 것을 관찰하였으며 이것은 XRD를 이용한 시료의 결정성 변화와 잘 일치하였다. (그림 2) 따라서 PL 발광강도는 격자이완에 의하여 생성된 결함에 의하여 영향을 받는 것을 알 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.124-125
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• 2007

Single crystal $CdGa_2Se_4$ layers were grown on a thoroughly etched semi-insulating GaAs(100) substrate at $420^{\circ}C$ with the hot wall epitaxy (HWE) system by evaporating the polycrystal source of $CdGa_2Se_4$ at $630^{\circ}C$ prepared from horizontal electric furnace. The photocurrent and the absorption spectra of $CdGa_2Se_4$/SI(Semi-Insulated) GaAs(100) are measured ranging from 293K to 10K. The temperature dependence of the energy band gap of the $CdGa_2Se_4$, obtained from the absorption spectra was well described by the Varshni's relation, $E_g$(T) = 2.6400 eV - $(7.721{\times}10^{-4}\;eV/K)T^2$/(T + 399 K). Using the photocurrent spectra and the Hopfield quasicubic model, the crystal field energy$({\Delta}cr)$ and the spin-orbit splitting energy$({\Delta}so)$ for the valence band of the $CdGa_2Se_4$ have been estimated to be 106.5 meV and 418.9 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1^-},\;B_{1^-},\;and\;C_{11^-}$ exciton peaks.

• Journal of Microbiology and Biotechnology
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• v.20 no.12
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• pp.1744-1749
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• 2010

The role of endophytic fungi in plant growth and development is well documented. However, endophytic fungi with growth promotion capacity have never been isolated from weeds previously. In the current study, we isolated 8 fungal endophytes from the roots of Monochoria vaginalis, a serious weed of rice paddy in Korea. These isolates were screened on Waito-C, in order to identify plant growth promoting metabolites. Two fungal isolates (M5.A & M1.5) significantly promoted the plant height and shoot length of Waito-C during preliminary screening experiments. The culture filtrates (CFs) of M5.A and M1.5 also promoted the shoot length of Echinocloa crusgalli. Gibberellins (GAs) analysis of the CFs of M5.A and M1.5 showed that these endophytic fungi secrete higher quantities of GAs as compared with wild-type G. fujikuroi KCCM12329. The CF of M5.A contained bioactive GAs ($GA_3$, 2.8 ng/ml; $GA_4$, 2.6 ng/ml, and $GA_7$, 6.68 ng/ml) in conjunction with physiologically inactive $GA_9$ (1.61 ng/ml) and $GA_{24}$ (0.18 ng/ml). The CF of M1.5 contained physiologically active GAs ($GA_3$, 1.64 ng/ml; $GA_4$, 1.37 ng/ml and $GA_7$, 6.29 ng/ml) in conjunction with physiologically inactive $GA_9$ (3.44 ng/ml), $GA_{12}$ (0.3 ng/ml), and $GA_{24}$ (0.59 ng/ml). M5.A and M1.5 were identified as new strains of Penicillium sp. and Aspergillus sp., respectively, based on their 18S rDNA sequence homology and phylogenetic analysis.

• The Korean Journal of Nuclear Medicine
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• v.28 no.3
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• pp.377-383
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• 1994

Objective : We retrospectively analysed $^{99m}Tc$-MDP bone and $^{67}Ga$ scans to evaluate therapeutic response of bone lymphoma among patients with complete remission. Subjects and Methods : We reviewed 35 cases with an increased uptake finding $^{99m}Tc$-MDP bone scans and 16 $^{67}Ga$ scans that were follow-up studies during and after therapy. The $^{99m}Tc$-MDP bone and $^{67}Ga$ scans were graded visually from 1 to 4 in which grade 3 means same uptake density as that of normal sacroiliac articulation in bone scan and normal liver in $^{67}Ga$ scan, respectively. Results: The improvement findings during and after therapy were found in 66.0% (19/ 29) and 72.7% (24/33) with $^{99m}Tc$-MDP bone scan, 84.6% (l1/13) and 86.7% (13/15) with $^{67}Ga$ scan, respectively. The mean grades of the uptake density in $^{99m}Tc$-MDP bone scan were 3.06 before, 2.34 during, 1.75 after therapy. Those in the $^{67}Ga$ scan were 3.22 before, 1.42 during 1.30 after therapy. Conclusion. $^{67}Ga$ scans appeared more sensitive than bone scans in evaluating therapeutic response of bone lymphoma.

• Nuclear Medicine and Molecular Imaging
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• v.40 no.3
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• pp.177-185
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• 2006

Purpose: Purpose of this study is to synthesize $^{99m}Tc$-labeled transferrin for injection imaging and to compare it with $^{67}Ga$-titrate for the detection of infectious foci. Materials and methods: Succinimidyl 6-hydrazino-nicotinate hydrochloride-chitosan-transferrin (Transferrin) was synthesized and radiolabeled with $^{99m}Tc$. Labeling efficiencies of $^{99m}Tc$-Transferrin were determined at 10 min, 30 min, 1 hr, 2 hr, 4 hr and 8 hr. Biodistribution and imaging studies with $^{99m}Tc$-Transferrin and $^{67}Ga$-citrate were performed in a rat abscess model induced with approximately $2{\times}10^8$ colony forming unit of Staphylococcus aureus ATCC 25923. Results: Successful synthesis of Transferrin was confirmed by mass spectrometry. Labeling efficiency of $^{99m}Tc$-Transferrin was $96.2{\pm}0.7%,\;96.4{\pm}0.5%,\;96.6{\pm}1.0%,\;96.9{\pm}0.5%,\;97.0{\pm}0.7%\;and\;95.5{\pm}0.7%$ at 10 min, 30 min, 1 hr, 2 hr, 4 hr and 8 hr, respectively. The injected dose per tissue gram of $^{99m}Tc$-Transferrin was $0.18{\pm}0.01\;and\;0.18{\pm}0.01$ in the lesion and $0.05{\pm}0.01\;and\;0.04{\pm}0.01$ in the normal muscle, and lesion-to-normal muscle uptake ratio was $3.7{\pm}0.6\;and\;4.7{\pm}0.4$ at 30 min and 3 hr, respectively. On image, lesion-to-background ratio of $^{99m}Tc$-Transferrin was $2.18{\pm}0.03,\;2.56{\pm}0.11,\;3.08{\pm}0.18,\;3.77{\pm}0.17,\;4.70{\pm}0.45\;and\;5.59{\pm}0.40$ at 10 min, 30 min, 1 hr, 2 hr, 4 hr and 10 hr and those of $^{67}Ga$-citrate was $3.06{\pm}0.84,\;4.12{\pm}0.54\;and\;4.55{\pm}0.74 $ at 2 hr, 24 hr and 48 hr, respectively. Conclusion: Transferrin is successfully labeled with $^{99m}Tc$, and its labeling efficiency was higher than 95% and stable for 8 hours. $^{99m}Tc$-Transferrin scintigraphy showed higher image quality in shorter time compared to $^{67}Ga$-citrate image. $^{99m}Tc$-transferrin is supposed to be useful in the detection of the infectious foci.