• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.10
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• pp.784-789
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• 1998

In this work, the optical properties of freestanding GaN single crystalline substrate grown by hydride vapor phase epitaxy(HVPE) were investigated. The low temperature PL spectrum in freestanding GaN consists of free and bound exciton emissions, and a deep DAP recombination around at 1.8eV. The optically-pumped stimulated emission in freestanding GaN substrate was observed at room temperature. At the maximum power density of 2MW/$\textrm{cm}^2$, the peak energy and FEHM of stimulated emission were 3.318 eV and 8meV, respectively. The excitation power dependence on the integrated emission intensity indicates the threshold pumping power density of 0.4 MW/$\textrm{cm}^2$.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.11
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• pp.71-78
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• 1995

Based on the popular 4-transistor SRAM cell, an analytical expression of the minimum cell ratio was derived by modeling the static read operation. By analyzing the relatively simple expression for the minimum cell ratio, which was derived assuming the ideal transistor characteristics, effects of the changes in supply voltage and process parameters on the minimum cell ratio was predicted, and the minimum power supply voltage for read operation was determined. The results were verified by simulations utilizing the suggested simulation method, which is suitable for monitoring the lower limit of supply voltage for proper cell operation. From the analysis, it was shown that the worst condition for cell operation is low temperature and low supply voltage, and that the operation margin can be effectively improved by reducing the threshold voltage of the cell transistors.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1254-1257
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• 2004

Comparative study on the effects of $H_2$ vs. $O_2$ plasma pretreatment of gate oxide on the degradation phenomenon of p-channel low-temperature polysilicon (LTPS) thin-film transistors (TFTs) were performed. After high drain current stress (HDCS) with $V_{gs}$ = $V_{ds}$, the p-channel TFTs pretreated by $O_2$ plasma showed increased immunity to the degradation of device characteristics such as threshold voltage and maximum field effect mobility because of the higher binding energy of Si-O bond than that of Si-H bond. The investigation of degradation phenomenon of these parameters with the applied power suggests that self-heating can be the major cause of degradation of polysilicon TFTs.

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.209-214
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• 2015

Silicon nitride films were deposited at $100^{\circ}C$ by using the catalytic chemical vapor deposition technique. The source gas mixing ratio, $R_N=[NH_3]/[SiH_4]$, was varied from 10 to 30, and the hydrogen dilution ratio, $R_H=[H_2]/[SiH_4]$, was varied from 20 to 100. The breakdown field strength reached a maximum value at $R_N=20$ and $R_H=20$, whereas the resistivity decreased in the same sample. The relative permittivity had a positive correlation with the breakdown field strength. The capacitance-voltage threshold curve showed an asymmetric hysteresis loop, which became more squared as $R_H$ increased. The width of the hysteresis window showed a negative correlation with the slope of the transition region, implying that the combined effect of $R_N$ and $R_H$ overides the interface defects while creating charge storage sites in the bulk region.

• Korean Journal of Remote Sensing
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• v.24 no.6
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• pp.571-581
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• 2008

The sea fog occurs frequently in the west coast of Korea in spring and summer. This study focused on the detection of sea fog using MODIS satellite images. We presented a method for sea fog detection based on the homogeneity level between low stratus and sea fog, which was that the top surface of sea fog had a homogeneous aspect while that of low stratus had a heterogenous aspect. The results showed that the both homogeneity of $11{\mu}m$ brightness temperature (BT) and brightness temperature difference (BTD, $BT_{3.7{\mu}m}-BT_{11{\mu}m}$) were available to discriminate sea fog from low stratus. The frequency of difference between BT in fog/stratus area and BT in clear area provided reasonable result. In addition, the threshold values of standard deviations of BT and BTD in the fog/stratus area were applicable to differentiate fog from low stratus.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.12
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• pp.1332-1336
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• 2004

Amorphous carbon (a-C) films have been deposited on Si(100) substrate using RF magnetron system in order to investigate the electron field emission properties. The a-C films were treated by $N_2$ gas plasma at room temperature. Surface morphologices and structural properties of the a-C films before and after $N_2$ plasma treatment were observed by scanning electron microscopy and Raman spectroscope, respectively. Structural properties and surface morphology of the a-C films were changed by $N_2$ plasma treatment. The emission properties can be improved by the plasma treatment according to the contents of nitrogen on the a-C films which is varied by plasma treatment time. Before the plasma treatment, the a-C films are found to have a threshold field of 14 V/$\mu$m, but the a-C film treated by $N_2$ plasma for 30 min exhibit threshold field as low as 6.5 V/$\mu$m.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.287.1-287.1
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• 2014

본 연구에서는 현재 디스플레이에서 가장 널리 이용되는 저온 polycrystalline silicon (poly-Si)의 결정화 방법에 따른 thin-film transistor (TFT)의 전기적 특성을 분석하였다. 분석에 이용된 결정화 방식은 Excimer Laser Annealing (ELA)와 Metal Induced Crystallization (MIC)이다. ELA와 MIC TFTs의 전기적 특성 측정을 통한 분석결과 ELA와 MIC poly-Si TFTs의 전기적 특성 [field-effect mobility (${\mu}_{FE}$), on/off current ratio ($I_{ON}/I_{OFF}$), sub-threshold swing (SS)]은 큰 차이는 없지만, ELA를 이용한 poly-Si TFT의 전기적 특성이 조금 우수하다. 하지만, MIC poly-Si TFT의 경우 threshold voltage ($V_{TH}$)가 0V에 보다 가까울 뿐만 아니라, 전기적 스트레스를 통한 신뢰성 확인 시 ELA poly-Si TFT보다 조금 더 안정적이다. 이는 ELA의 경우 좁은 면에 선형 레이저 빔으로 조사하면서 생기는 hill-lock의 영향으로 표면이 거칠고 균일하지 못하여 바이어스 인가시 생기는 문제이다. 또한 MIC는 금속 촉매를 이용해 결정립 경계를 확장하고 결정 크기를 키워 대면적화에 유리하다. Thermal Stress에서는 (from 293K to 373K) TFT에 점차 높은 온도를 가하자 MIC poly-Si TFT의 경우 off 상태에서 누설 전류 값이 증가하며 열에 민감한 반응을 보이는 것을 확인하였다.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1289-1291
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• 1993

The hydrogenation effects on characteristics of polycrystalline silicon thin film transistors(poly-Si TFT's) of which the channel length varies from $2.5{\mu}m\;to\;20{\mu}m$ and poly-Si layer thickness is 50, 100, and 150 nm was investigated. After 1 hr hydrogenation annealing by PECVD, the threshold voltage shift decreased dependent on the channel length, but channel width may not alter the threshold voltage shift. In addition to channel length, the active poly-Si layer thickness may be an important parameter on hydrogenation effects, while gate poly-Si thickness may do not influence on the characteristics of TFT's. Considering our experimental results, we propose that channel length and active poly-Si layer thickness may be a key parameters of hydrogenation of poly-Si TFT's.

• Korean journal of applied entomology
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• v.52 no.4
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• pp.295-304
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• 2013

This study aimed to understand the physiological status of the beet armyworm, Spodoptera exigua at low developmental threshold temperature (LTT) through analysis of gene-expression patterns associated with different functions (metabolism, nervous system, immune, and stress). The estimated LTTs for egg, larval, and pupal developments varied with $5.5{\sim}11.6^{\circ}C$. Larvae were able to develop at the lower temperatures than eggs and pupae. However, the physiological LTT ($15^{\circ}C$) in the fifth instar was much higher than the estimated LTT ($10.3^{\circ}C$). Gene expression patterns estimated by a quantitative RT-PCR (qRT-PCR) indicate that most genes in different functional groups increased their expressions with increase of larval instars. In the same fifth instar, as the treatment temperatures increased, the gene expression levels increased. Moreover, the newly molted fifth instar larvae were different in their gene expression rates according to their previous culturing temperatures. Most gene expressions were suppressed in the fifth instar larvae at the physiological LTT ($15^{\circ}C$). However, the larvae at $15^{\circ}C$ gradually exhibited significant increase in the gene expression rates with rearing time just like those at the higher temperature. These results suggest that S. exigua at LTT exhibits a typical gene expression pattern with maintaining significantly suppressed levels.

• Korean journal of applied entomology
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• v.51 no.4
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• pp.371-376
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• 2012

This study was conducted to predict the hatching time of eggs of Lycorma delicatula, to select an effective environmentally-friendly agriculture material (EFAM) and to evaluate the attraction effect of brown sticky traps for controling of Lycorma delicatula nymph and adults. Eggs hatched 55.9, 26.8, 21.6 days after incubation at 15, 20, $25^{\circ}C$ with 14L:10D condition and the hatching rates of egg were 61.9, 57.8, 30.4%, respectively. At high temperature conditions, egg development periods were shorter and the hatching rate was lower. The relationship between temperature and developmental rate was expressed by the linear equation Y=0.0028X-0.0228, $R^2$=0.9561. The low temperature threshold of eggs was $8.14^{\circ}C$ and the thermal constant required to reach larva was 355.4 DD. According to this relationship, the mean estimated hatching date was $22^{nd}$ May. The effective EFAM was natural plant extract, sophora extract, derris extract to nymph and natural plant extract, pyrethrum extract, sophora extract to adult. Among three colors of sticky trap : brown, blue and yellow, the brown sticky trap was the most attractive to nymphs and adults of L. delicatula over a 2 weeks trial period. It suggested that the brown sticky trap could be a very useful and environment-friendly control method for nymphs and adults of L. delicatula.