• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.10
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• pp.9-16
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• 1999

When the conventional IPD (inter-poly-dielctrics) layer with ONO(oxide-nitride-oxide) structure was used in the Flash EEPROM cell, its data retention characteristics were significanfly degraded because the top oxide of the ONO layer was etched off due to the cleaning process used in the gate oxidation process for the peripheral MOSFETs. When the IPD layer with the ONON(oxide-nitride-oxide-nitride) was used there, however, its data retention characteristics were much improved because the top nitride of the ONON layer protected the top oxide from being etched in the cleaning process. For the modelling of the data retention characteristics of the Flash EEPROM cell with the ONON IPD layer, the decrease of the threshold voltage cue to the charge loss during the bake was here given by the empirical relation ${\Delta}V_t\; = \;{\beta}t^me^{-ea/kT}$ and the values of the ${\beta}$=184.7, m=0.224, Ea=0.31 eV were obtained with the experimental measurements. The activation energy of 0.31eV implies that the decrease of the threshold voltage by the back was dur to the movement of the trapped electrons inside the inter-oxide nitride layer. On the other hand, the results of the computer simulation using the model were found to be well consistent with the results of the electrical measurements when the thermal budget of the bake was not high. However, the latter was larger then the former in the case of the high thermal budger, This seems to be due to the leakage current generated by the extraction of the electrons with the bake which were injected into the inter-oxide niride later and were trapped there during the programming, and played the role to prevent the leakage current. To prevent the generation of the leakage current, it is required that the inter-oxide nitride layer and the top oxide layer be made as thin and as thick as possible, respectively.

• KIPS Transactions on Software and Data Engineering
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• v.2 no.4
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• pp.267-272
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• 2013

As an important operation with many applications such as data cleaning and duplicate detection, the similarity join is a challenging issue, which finds all pairs of records whose similarities are above a given threshold in a dataset. We propose a new algorithm that uses the prefix filtering principle as strong constraints on generation of candidate pairs for fast similarity joins. The candidate pair is generated only when the current prefix token of a probing record shares one prefix token of an indexing record within the constrained prefix tokens by the principle. This generation method needs not to compute an upper bound of the overlap between two records, which results in reduction of execution time. Experimental results show that our algorithm significantly outperforms the previous prefix filtering-based algorithms on real datasets.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.1
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• pp.56-59
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• 2020

Porcelain insulators are typically exposed to surface discharge and lightning impulse in service. This study investigates the insulation characteristics of the external and internal discharges of a porcelain insulator with respect to its flashover for a 154 kV transmission line. The experiments are also conducted using a wet flashover test and an impulse test based on the external discharge and the internal penetration, to classify the flashover voltage-time curve of the porcelain insulator. When an impulse with a strength of 2,500 kV/㎲ was applied three times to 6.5 mm ceramic samples, electrical penetration of approximately 70% occurred. The impulse experiment confirmed that the electrical penetration inside the porcelain insulator coincided with the area where the electric field was concentrated. The wet flashover voltage test revealed that the flashover threshold voltage increases by approximately 7% after cleaning of the surface.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.4 no.2
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• pp.198-207
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• 1994

In order to evaluate the effectiveness of environmental intervention of work place, metal mercury concentration in air and in urine of the total 43 workers for 3years from December 1991 to October 1993 in a fluorescent lamp manufacturing industry exposed to mercury, was measured before and after implementation of controls such as establishing exhaust ventilation at the department of exhaustion, coating the floor of work place with epostane, cleaning of the floor, improved housekeeping, and etc. The results were as follows. 1. Before the intervention(December 1991) 39.0% exceeded metal mercury Threshold Limit Value(TLV, $0.05mg/m^3$). After the intervention(October 1993) 10.0% exceeded TLV and geometric mean of mercury in air was $0.1mg/m^3$, and showed effectiveness rate of intervention to be 74.4% 2. After the intervention, geometric means of mercury concentrations in air were 0.013, $0.019mg/m^3$ and showed effectiveness rate of intervention to be 76.6%, 65.5% in A factory(right tube lamp)and at exhaustion department, respectively, A follow up survey fround statistically significant reductions in mercury concetration in air three years later. 3. Mercury concentration in urine of 11 workers(29.7%) exceeded warning level of $100{\mu}l/l$ before the intervention. After the intervention, of 3workers(8.8%) exceeded warning level and geometric mean of mercury concentration($26.5{\mu}l/l$) in urine was 2.4 times than that of before the intervention. Geometric means of mercury concentrations in urine of workers at exhaustion department, at sealing and aging department were 44.0, $77.7{\mu}l/l$, respectively and they decreased 2.3, 3.2 times than that of before the intervention.

• Proceedings of the Korean Vacuum Society Conference
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• 1998.02a
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• pp.71-72
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• 1998

반도체 집적 공정의 발달로 차세대 소자용으로 30 A 이하의 극 박막 Si02 절연막이 요구되고 있으며, 현재 제품으로 50-70 A 두께의 절연막을 사용한 것이 발표되고 있다. 절연막의 두께가 앓아질수록 많은 문제가 발생할 수 있는데 그 예로 절연막의 breakdo때둥에 의한 신뢰성 특성의 악화, 절연막올 통한 direct tunneling leakage current, boron풍의 dopant 침투로 인한 소자 특성 ( (Threshold Voltage)의 불안, 전기적 stress하에서의 leakage current증가와 c charge-trap 및 피terface s쩌.te의 생성으로 인한 소자 특성의 변화 둥으로 요약 된다. 절연막의 특성올 개선하기 위해 여러 가지 새로운 공정들이 제안되었다. 그 예로, Nitrogen올 Si/Si02 계면에 doping하여 절연막의 특성을 개선하는 방법 으로 고온 열처 리 를 NH3, N20, NO 분위 기 에서 실시 하거 나, polysilicon 또는 s silicon 기판에 nitrogen올 이온 주입하여 열처리 하는 방법, 그리고 Plasma분 위기에서 Nitrogen 함유 Gas를 이용하여 nitrogen을 doping시키는 방법 둥이 연구되고 있다. 또한 Oxide cleaning 후 상온에서 성장되는 oxide를 최소화 하여 절연막의 특성올 개선하기 위하여 LOAD-LOCK을 이용하는 방법, C뼈피ng 공정의 개선올 통한 contamination 감소와 silicon surface roughness 감소 로 oxide 신뢰성올 개선하는 방법 둥이 있다. 구조적 인 측면 에 서 는 Polysilicon 의 g없n size 를 최 적 화하여 OxideIPolysilicon 의 계면 특성올 개선하는 연구와 Isolation및 Gate ETCH공정이 절연막의 특성에 미 치 는 영 향도 많이 연구되 고 있다 .. Plasma damage 가 Oxide 에 미 치 는 효과 를 제어하는 방법과 Deuterium열처리 퉁올 이용하여 Hot electron Stress하에서 의 MOS 소자의 Si/Si02 계면의 신뢰성을 개선하고 있다. 또한 극 박막 전연막의 신뢰성 특성올 통계적 분석올 통하여 사용 가능한 수명 올 예 측 하는 방법 과 Direct Tunneling Leakage current 를 고려 한 허 용 가농 한 동작 전 압 예측 및 Stress Induced Leakage Current 둥에 관해서 도 최 근 활발 한 연구가 진행되고 있다.

• Membrane and Water Treatment
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• v.6 no.1
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• pp.77-94
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• 2015

Ultrafiltration membranes have several advantages over conventional drinking-water treatment. However, this technology presents major limitations, such as irreversible fouling and low removal of natural organic matter. Fouling depends heavily on the raw-water quality as well as on the operating conditions of the process, including flux, permeate recovery, pre-treatment, chemical cleaning, and backwashing. Starting with the premise that the optimisation of operating variables can improve membrane performance, different experiments were conducted in a pilot plant located in Granada (Spain). Several combinations of permeate and backwashing flow rates, backwashing frequencies, and aeration flow rates were tested for low-quality water coming from Genil River with the following results: the effluent quality did not depend on the combination of operating conditions chosen; and the membrane was effective for the removal of microorganisms, turbidity and suspended solids but the yields for the removal of dissolved organic carbon were extremely low. In addition, the threshold transmembrane pressure (-0.7 bar) was reached within a few hours and it was difficult to recover due to the low efficiency of the chemical cleanings. Moreover, greater transmembrane pressure due to fouling also increased the energy consumption, and it was not possible to lower it without compromising the permeate recovery. Finally, the intensification of aeration contributed positively to lengthening the operation times but again raised energy consumption. In light of these findings, the feasibility of ultrafiltration as a single treatment is questioned for low-quality influents.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.2
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• pp.381-389
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• 2004

To investigate changes of multi-purpose solutions for soft contact lens(MPS) depending on using period or keeping temperature, we evaluate four brands of MPS. No significant difference was seen in protein deposit removing efficacy after samples had used for 24 weeks and kept at $4^{\circ}C$, $20^{\circ}C$ or $30^{\circ}C$. The pH values of the samples of 4 brands measured weekly over the 24 week testing period. The initial average pH value of samples were 7.0, 7.5, 7.6 or 8.2. One brand of MPS was in the range of the threshold for ocular awareness, which is outside the zone of 6.6 ~ 7.8. During the testing period, the pH value were decreased in using period-dependent manner. At the 24th week, the average pH values of samples turned to 6.6, 7.2, 7.2 or 7.7. However, the difference of keeping temperature was not associated with decreased levels of pH values. After 24 weeks, one of total 36 samples was contaminated by bacteria. Furthermore, the change of components was shown after 24 weeks in the analysis using thin layer chromatography and the analysis of UV absorption pattern. The results of our study provides that the keeping temperature of MPS is not the important factor of changes of MPS, but the using period of MPS can cause contact lens wearers discomfort.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.15 no.2
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• pp.90-103
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• 2005

Objective: This study was carried out to assess the status of working environments, to improve the working environments, and to be helpful to prevent occupational disease. Methods: The authors measured the noise level, concentration of dust, heavy metals, organic solvents, and other chemicals at 95 industries (22 working processes) by type of working process in manufacturing industry of parts and accessories for motor vehicles and its engines from January to December 2003. Samples were measured and analyzed by regulations of Korea Ministry of Labor, manuals of National Institute for Occupational Safety and Health (NIOSH) and Occupational Safety and Health Administration (OSHA). Results: Results are as follows. 1. Major processes exceeding mean noise levels provided the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) were shakeout [97.5 dB(A)]. shot-blast [94.2 dB(A)], pressing [92.9 dB(A)], crushing [91.2 dB(A)], and cleaning [90.6 dB(A)]. 2. Mean concentrations of dusts were not exceeded to the TLV. But concentration on some points of processes as like welding (6.50 mg/m3), foundry (5.24 mg/m3) were exceeded. 3. Mean concentrations of heavy metals were not exceeded to the TLV. 4. Mean concentrations of organic solvents and chemicals were not exceeded to the TLV. 5. Improving rate for working environment were significantly higher in industries with health manager than without (p<0.05), and by increasing the year of working environmental measurement (p<0.01). Conclusions: The results suggest that working processes of exceeding to the TLV will be needed rapid improvement of the working environment, and also the others will be needed positive management of the working environment. Health managers must be recommended to employ in the workplace, and further studies for relationship between working environment and health effects for the workers must be carried out.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.344-344
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• 2014

Transparent amorphous oxide semiconductors such as a In-Ga-Zn-O (a-IGZO) have advantages for large area electronic devices; e.g., uniform deposition at a large area, optical transparency, a smooth surface, and large electron mobility >10 cm2/Vs, which is more than an order of magnitude larger than that of hydrogen amorphous silicon (a-Si;H).1) Thin film transistors (TFTs) that employ amorphous oxide semiconductors such as ZnO, In-Ga-Zn-O, or Hf-In-Zn-O (HIZO) are currently subject of intensive study owing to their high potential for application in flat panel displays. The device fabrication process involves a series of thin film deposition and photolithographic patterning steps. In order to minimize contamination, the substrates usually undergo a cleaning procedure using deionized water, before and after the growth of thin films by sputtering methods. The devices structure were fabricated top-contact gate TFTs using the a-IGZO films on the plastic substrates. The channel width and length were 80 and 20 um, respectively. The source and drain electrode regions were defined by photolithography and wet etching process. The electrodes consisting of Ti(15 nm)/Al(120 nm)/Ti(15nm) trilayers were deposited by direct current sputtering. The 30 nm thickness active IGZO layer deposited by rf magnetron sputtering at room temperature. The deposition condition is as follows: a rf power 200 W, a pressure of 5 mtorr, 10% of oxygen [O2/(O2+Ar)=0.1], and room temperature. A 9-nm-thick Al2O3 layer was formed as a first, third gate insulator by ALD deposition. A 290-nm-thick SS6908 organic dielectrics formed as second gate insulator by spin-coating. The schematic structure of the IGZO TFT is top gate contact geometry device structure for typical TFTs fabricated in this study. Drain current (IDS) versus drain-source voltage (VDS) output characteristics curve of a IGZO TFTs fabricated using the 3-layer gate insulator on a plastic substrate and log(IDS)-gate voltage (VG) characteristics for typical IGZO TFTs. The TFTs device has a channel width (W) of $80{\mu}m$ and a channel length (L) of $20{\mu}m$. The IDS-VDS curves showed well-defined transistor characteristics with saturation effects at VG>-10 V and VDS>-20 V for the inkjet printing IGZO device. The carrier charge mobility was determined to be 15.18 cm^2 V-1s-1 with FET threshold voltage of -3 V and on/off current ratio 10^9.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.5
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• pp.316-325
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• 2012

In this study, we suggested adequate control technology by analyzing emission process and main chemical of VOC/HAPs generated from four paint factories in Busan area. And we estimated whether Kapok fiber, which is a natural material, can be commercially used for an absorbent by testing adsorption ability. As a result of this sturdy, above 60% of VOC/HAPs was volatilized and dispersed inside the working place without conducting control system of facilities during manufacturing paints. Concentration profile of VOC/HAPs, which is volatile naturally outside the factories, is surveyed above 70% at Toluene, Ethylbenzene, and Xylene. And a result of evaluation of odor attribution level about the component whose Odor Threshold is known, it is estimated that major cause material of A, B, C factories is Toluene and that of D factory is m/p-Xylene. And that result presented design arguments such as facilities specifications, activated carbon filling volume, and replace cycle of activated carbon as control technology. Also, that result presented emission process improvement such as adsorption of central-controlled ventilation device, installation of inlet flenge, and potable cleaning process. The rate of pollutant adsorption of Kapok fiber, which is natural material, is indicated about 91.9%, 66.7%. That result validated the possibility as replacement of activated carbon.