• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.65-65
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• 1999

Dry etching technique provides more easy controllability on the etch profile such as anisotropic etching than wet etching process and the results of lots of researches on the characterization of various plasmas or ion beams for semiconductor etching have been reported. Chlorine-based plasmas or chlorine ion beam have been often used to etch several semiconductor materials, in particular Si-based materials. We have studied the effect of He flow rate on the Si and SiO2 dry etching using chlorine-based plasma. Experiments were performed using reactive ion etching system. RF power was 300W. Cl2 gas flow rate was fixed at 58.6 sccm, and the He flow rate was varied from 0 to 120 sccm. Fig. 1 presents the etch depth of si layer versus the etching time at various He flow rate. In case of low He flow rate, the etch rate was measured to be negligible for both Si and SiO2. As the He flow increases over 30% of the total inlet gas flow, the plasma state becomes stable and the etch rate starts to increase. In high Ge flow rate (over 60%), the relation between the etch depth and the time was observed to be nearly linear. Fig. 2 presents the variation of the etch rate depending on the He flow rate. The etch rate increases linearly with He flow rate. The results of this preliminary study show that Cl2/He mixture plasma is good candidate for the controllable si dry etching.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.23-30
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• 1997

Semiconductive SrTiO3 ceramic bodies were prepared by conventional ceramic powder processes in-cluding sintering in a reducing atmosphere. Sodium or potassium ions were diffused from the surface of the sintered bodies into the inner region using thermal diffusion process at 800-120$0^{\circ}C$. The effects of such ther-mal treatments on the electrical and chemical characteristics of the grain boundaries were investigated. The presence of sodium or potassium ions at grain boundaries produces non-linear current-voltage behaviors, electrical boundary potential barriers of 0.1-0.2eV, and threshold voltages of 10-70V. The diffused ions form diffusion layers with thicknesses of 20-50nm near the grain boundaries, reducing the concentration of strontium and oxygen.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.12
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• pp.46-53
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• 2003

This paper describes a new linear operational transconductance amplifier (OTA) and its application to the 9th-order Bessel filter. To improve the linearity of the OTA, we employ a mobility compensation technique. The combination of the triode and the subthreshold region transistors can compensate the mobility reduction effect and make the OTA with a good linearity. The proposed OTA shows $\pm$0.32% Gm variation over the input range of $\pm$0.8-V. The total harmonic distortion (THD) was lower than -60-㏈. The 9th-order Bessel filter has been designed using a 0.35-${\mu}{\textrm}{m}$ n-well CMOS process under 3.3-V supply voltage. It shows the cutoff frequency of 8-MHz and the power consumption of 65-mW.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.1
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• pp.61-70
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• 2008

This paper presents the flexible MEMS transmitter based on flexible printed circuit board or FPCB, which can be transformed to arbitrary shape. The FPCB is suitable to fabricate light weight and small size modules with the help of its thin thickness. Moreover a module based on FPCB can be attached on the arbitrary curved surface due to its flexible enough to be lolled up like paper. In this paper, the flexible MEMS transmitter integrated on FPCB for a short-distance sensor network which is based on orthogonal frequency division multiplexing(OFDM) communication system is proposed. The active device of the proposed flexible MEMS transmitter is fabricated on InGaP/GaAs HBT process which has been used for power amplifier design to take advantages of high linear and high efficient characteristics. Moreover, the passive devices such as the filter and signal lines are integrated and fabricated on the FPCB board. The performance of the fabricated flexible MEMS transmitter is analyzed with EVM characteristics of the output signal.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.7
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• pp.620-626
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• 2015

In this paper, a 2~6 GHz wideband GaN power amplifier MMIC is designed and fabricated using a second-order all-pass filter for input impedance matching and an LC parallel resonant circuit for minimizing an output reactance component of the transistor. The second-order all-pass filter used for wideband lossy matching is modified in an asymmetric configuration to compensate the effect of channel resistance of the GaN transistor. The power amplifier MMIC chip that is fabricated using a $0.25{\mu}m$ GaN HEMT foundry process of Win Semiconductors, Corp. is $2.6mm{\times}1.3mm$ and shows a flat linear gain of about 13 dB and input return loss of larger than 10 dB. Under a saturated power mode, it also shows output power of 38.6~39.8 dBm and a power-added efficiency of 31.3~43.4 % in 2 to 6 GHz.

• Journal of Korean Elementary Science Education
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• v.30 no.4
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• pp.468-481
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• 2011

This research is to observe and analyze the student interactions when inquiry problems were generated along with the students by using asynchronous discussion methods with the class bulletin board. For this research, 10 students from a single class of 6th grade were selected. The subject students were divided into 2 groups by cognitive levels. After the students were submitted the 4 problem situations for 1 week each, the discussion process was analyzed. The research results are as follows. First, the analysis of the step by step interactive discussion showed that several students answered for the question from a single student while discussing first for the question and answer in a form of a question with many multiple answers without any connections with the previously asked questions. At the end of the discussion, one to two students answered to a question by taking turns and the type of discussion changed to one question - one answer type by answering to the person who spoke prior to the next. Second, the discussion took place with the students in the transitional stage speaking in time in order, to provide comments to the bottom of the linear form and students in the formal operational stage students speaking in temporal order, regardless of the number of comments in the direction of the radiation(mind map) forms. The individual comment speaking rates were similar in the two groups so the students were able to speak indiscriminately.

• Journal of Ecology and Environment
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• v.34 no.4
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• pp.401-410
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• 2011

We assayed the effects of simulated acid rain on the mass loss, $CO_2$ evolution, dehydrogenase activity, and microbial biomass-C of decomposing Sorbus alnifolia leaf litter at the microcosm. The dilute sulfuric acid solution composed the simulated acid rain, and the microcosm decomposition experiment was performed at 23$^{\circ}C$ and 40% humidity. During the early decomposition stage, decomposition rate of S. alnifolia leaf litter, and microbial biomass, $CO_2$ evolution and dehydrogenase activity were inhibited at a lower pH; however, during the late decomposition stage, these characteristics were not affected by pH level. The fungal component of the microbial community was conspicuous at lower pH levels and at the late decomposition stage. Conversely, the bacterial community was most evident during the initial decomposition phase and was especially dominant at higher pH levels. These changes in microbial community structure resulting from changes in microcosm acidity suggest that pH is an important aspect in the maintenance of the decomposition process. Litter decomposition exhibited a positive, linear relationship with both microbial respiration and microbial biomass. Fungal biomass exhibited a significant, positive relationship with $CO_2$ evolution from the decaying litter. Acid rain had a significant effect on microbial biomass and microbial community structure according to acid tolerance of each microbial species. Fungal biomass and decomposition activities were not only more important at a low pH than at a high pH but also fungal activity, such as $CO_2$ evolution, was closely related with litter decomposition rate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.635-640
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• 2016

This paper dealt with the deterioration characteristics and an on-line diagnosis equipment for SPDs (surge protective devices). An accelerated aging test was carried out using a $8/20{\mu}s$ standard lightning impulse current to analyze the changes of electrical characteristics and to propose the diagnostic parameters and the criterion for deterioration of ZnO varistor which is the core component of SPDs. Based on the experimental results, an on-line diagnosis equipment for SPD was fabricated, which can measure the total leakage current, reference and clamping voltage. The leakage current measurement circuit was designed using a low-noise amplifier and a clamp type ZCT. A linear controller, the leakage current measurement part and a HVDC were used in the measurement of reference voltage. The measurement circuit of clamping voltage consisted of a surge generator and a coupling circuit. In a calibration process, measurement error of the prototype equipment was less than 3%.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1114-1123
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• 2015

Bushing is the key link to connect outer and inner insulating systems and also the essential electric accessory in electric power system, especially in the high voltage engineering (AC 1000kV, DC 800kV). This paper presented the experimental research of thermal aging characteristic of oil-paper insulation used in bushing. A thermally accelerated aging experiment at 90℃ was performed. The bushing models containing five layers of paper were sealed into the aging vessels and further aged for 250 days. Then several important parameters associated with the aging were observed and evaluated. The results showed that the degree of polymerization (DP) of papers gradually decreased. The DP values of outermost layer and middle layer fit well into the second-order kinematic model and first-order kinematic model, respectively. Less deterioration speed of the inter-layer paper than outer layer was confirmed by the variation of DP. Hydrolysis was considered as the main cause to this phenomenon. In addition, the logarithm of the furfural concentrations in insulation oil was found to have good linear relationship with DP of papers. Interestingly, when the aging time is about 250 days and DP is 419, the aging process reaches an inflection point at which the DP approaches the leveling off degree of polymerization (LODP) value. Both tanδ and acid number of oils increased, while surface and volume resistivity of papers decreased. The obtained results demonstrated that thermal aging and moisture absorbed in papers brought great influence to the degradation of insulating paper, leading to rapid decrease of DP and increase of the tanδ. Thus, the bushing should be avoided from damp and real-time monitoring to the variation of tanδ and DP values of paper is an effective way to evaluate the insulation status of bushing.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1295-1296
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• 2008

Hydrogen peroxide ($H_2O_2$) biosensor is one of the most developing sensors because this kind of sensors is highly selective and responds quickly to the specific substrate. Hemoglobin (Hb) has been used as ideal biomolecules to construct hydrogen peroxide biosensors because of their high selectivity to $H_2O_2$. The direct electron transfer of Hb has widely investigated for application in the determination of $H_2O_2$ because of its simplicity, high selectivity and intrinsic sensitivity. An electrochemical detection for hydrogen peroxide was investigated based on immobilization of hemoglobin on DNA/Fe(pyterpy)$^{2+}$ modified gold electrode. The pyterpy monolayers were firstly an electron deposition onto the gold electrode surface of the quartz crystal microbalance (QCM). It is offered a template to attach negatively charged DNA. The fabrication process of the electrode was verified by quartz crystal analyzer (QCA). The experimental parameters such as pH, applied potential and amperometric response were evaluated and optimized. Under the optimized conditions, this sensor shows the linear response within the range between $3.0{\times}10^{-6}$ to $9.0{|times}10^{-4}$ M concentrations of $H_2O_2$. The detection limit was determined to be $9{\times}10^{-7}$ M (based on the S/N=3).