Sung Ho Hwang

Deep Trench Isolation for Crosstalk Suppression in Active Pixel Sensors with 1.7 µm Pixel Pitch

A deep trench isolation (DTI) process with a 4 µm deep trench has been developed and successfully applied to 5-megapixel complementary metal oxide silicon (CMOS) image sensors with a 1.7 µm pixel pitch. It was found that from the results of simulations and experiments, DTI is very effective for reducing electrical crosstalk without degrading other pixel characteristics, such as full well capacity, sensitivity, and white spot density. Therefore, DTI could be a solution for obtaining a high performance for CMOS image sensors with a small pixel size of sub-2.0 µm.

Relationship between culturable airborne bacteria concentrations and ventilation systems in underground subway stations in Seoul, South Korea

In this study, we evaluated the concentrations of culturable airborne bacteria (CABs) in the underground environment of 16 subway stations in Seoul, South Korea. The effects of environmental factors on CAB distributions and concentrations, including temperature, relative humidity, depth, year of construction, number of subway passengers, and ventilation, were investigated. Tryptone soy agar was used as the culture medium. Isolated bacteria were initially characterized according to cell morphology and Gram staining and then further characterized using the VITEK 2 XL microbial identification system. There were significant correlations between CAB concentrations and station temperature, depth, and construction year. Micrococcus and Staphylococcus species accounted for 66xa0% of the total number of CABs identified. CAB concentrations in stations with ventilation systems were significantly lower than those in stations without ventilation systems (pu2009<u20090.001). Thus, it is critical to develop techniques to improve indoor air quality in subway stations with no ventilation system.

The Features and Characteristics of 5-mega CMOS Image Sensor with Topologically Unique 1.7/spl m/m~1.7/spl mu/m Pixels

CMOS image sensor (CIS) of 5-mega pixel density has been successfully developed with the smallest pixels (1.7mumtimes1.7mum) ever made. The newly introduced unique pixel architecture brought excellent optical symmetry and high electron capacity. Degradation of sensitivity and cross-talk can be suppressed with the optimization of the optical structure through proper color filter material and reduction of total aspect ratio (vertical stack height/pixel pitch) with Cu back end of line (BEOL)

Concentrations of PM10 and airborne bacteria in daycare centers in Seoul relative to indoor environmental factors and daycare center characteristics

The purpose of this study was to measure concentrations of PM10 and airborne bacteria (AB) to determine how each one of them correlated with particular indoor environmental factors and characteristics of daycare centers in Seoul, South Korea.PM10 and AB were sampled in 330 daycare centers in the middle of a classroom, along with measurements of temperature and relative humidity. Spearman’s correlation and Mann-Whitney analyses were used to examine the relationship among and differences between PM10 concentration, AB concentration, indoor environmental factors, and daycare center characteristics.There were significant correlations between PM10 concentration and AB concentration (ru2009=u20090.128, pu2009<u20090.05), temperature (ru2009=u20090.153, pu2009<u20090.01), and relative humidity (ru2009=u20090.185, pu2009<u20090.01). PM10 concentrations with two or more windows; a heating, ventilation, and air conditioning (HVAC) system; and the use of air purifier were lower than concentrations with one window, window ventilation only, and no air purifier. AB concentrations were significantly higher when daycare centers had only one window and used only window ventilation (pu2009<u20090.05).Though there are many uncontrollable outdoor environmental factors that influence air quality, we demonstrated that using an HVAC system and an air purifier significantly reduces PM10 concentrations and is a practical change that could be implemented to improve the indoor air quality of daycare centers.

Seasonal variation in airborne endotoxin levels in indoor environments with different micro-environmental factors in Seoul, South Korea.

This study evaluated the variation over a year in airborne endotoxin levels in the indoor environment of five university laboratories in Seoul, South Korea, and examined the micro-environmental factors that influenced endotoxin levels. These included temperature, relative humidity, CO2, CO, illumination, and wind velocity. A total of 174 air samples were collected and analyzed using the kinetic limulus amebocyte lysate assay. Endotoxin levels ranged from <0.001 to 8.90EU/m(3), with an overall geometric mean of 0.240EU/m(3). Endotoxin levels showed significantly negative correlation with temperature (r=-0.529, p<0.001), CO2 (r=-0.213, p<0.001) and illumination (r=-0.538, p<0.001). Endotoxin levels tended to be higher in winter. Endotoxin levels in laboratories with rabbits were significantly higher than those of laboratories with mice. Multivariate regression analysis showed that the environmental factors affecting endotoxin levels were temperature (coefficient=-0.388, p<0.001) and illumination (coefficient=-0.370, p<0.001). Strategies aimed at reducing airborne endotoxin levels in the indoor environments may be most effective if they focus on illumination.

Erratum to: Concentrations and identification of culturable airborne fungi in underground stations of the Seoul metro

The purpose of this study was to measure the culturable airborne fungi (CAF) concentrations in the underground subway stations of Seoul, Korea at two time points. This study measured the CAF concentrations in enclosed environments at 16 underground stations of the Seoul Metro in 2006 and 2013 and investigated the effects of various environmental factors, including the presence of platform screen doors, temperature, relative humidity, and number of passengers. CAF concentrations at the stations in 2006 were significantly higher than that at the same stations in 2013 (pxa0<xa00.001). Furthermore, there was a significant correlation between CAF concentration and relative humidity (rxa0=xa00.311, pxa0<xa00.05). Geotrichum and Penicillium were the predominant genera. The CAF concentrations in stations with an operating supply air were significantly higher than that in stations with no supply air (pxa0<xa00.001). Therefore, it is recommended that special attention be given to stations with clean supplied air to improve the indoor air quality of these subway stations.

Radon and NO 2 levels and related environmental factors in 100 underground subway platforms over two-year period

In this study, the environmental factors that affect radon (Rn) and nitrogen dioxide (NO2) levels in subway-station underground platforms are evaluated, and the outdoor NO2 levels are compared with those obtained for the underground platforms. The Rn and NO2 levels from May 2013 to September 2015 are determined for lines 1-4 of the Seoul Metro, via calculation of the arithmetic means of the Rn and NO2 levels with their standard deviations (SDs). The underground Rn levels in 2013 are found to be significantly higher than those recorded in 2015 for the Seoul Metro. In addition, the Rn levels are related to the station depth and construction year. Further, the underground NO2 levels are shown to be significantly higher than the outdoor levels for all four Seoul Metro subway lines. The Rn levels are also found to vary significantly between months, and are shown to increase gradually with depth from 8 to 20xa0m. The Rn levels are also higher for stations constructed in the 1980s. Therefore, stricter monitoring of Rn level may be required for stations constructed in the 1980s and/or having platform depths within the 8-20xa0m range. Island-type platform stations based on granite areas may also require careful attention.

Exposure assessment of particulate matter and blood chromium levels in people living near a cement plant

This study evaluates the effect of air pollution caused by cement plants on nearby residential areas and performs an exposure assessment of particulate matter (PM) and total Cr, Cr6+, Pb, and Al. Further, the blood Cr levels of residents exposed to PM released by cement plants are also assessed. Nine buildings (eight residential and one elementary school building) close to cement plants were selected for this study, which were located in Pyeongtaek port, in west of Gyeonggi Province, South Korea. A total of 51 suspended particulate samples were collected at a flow rate of 2.0xa0L/min. Total Cr was more widely detected in residents’ houses and elementary schools. PM levels were higher at distances of 4.1 and 4.8xa0km than those at closer distances of 2.7xa0km. This was due to the influence of wind direction. The estimated mean blood level of Cr for the study participants was 3.80xa0μg/L, which is higher than levels estimated by other studies on Cr blood levels. Therefore, cement plants could cause an increase in total Cr and blood Cr levels in residential areas, and more continuous monitoring is necessary to better understand their impacts.

Comparison of the relative performance efficiencies of melt-blown and glass fiber filter media for managing fine particles

ABSTRACT The purpose of this study was to compare the performance efficiency of melt-blown and currently used glass fiber filter media under the same environmental conditions. To evaluate filter efficiency, filter class was determined according to ISO and European standards (EN 1822-1:2009) using an automated filter tester (0.3 μm size), taking into account particle filtration, fractional efficiency for negative pressure devices, and consumption of electrical power. The average fractional efficiency, quality factor (QF), fractional efficiency by dust loading amount, pressure by dust loading amount, and QF by dust loading amount were higher in the case of melt-blown media than in the case of glass fiber filters. The fractional efficiency of hydrocharged melt-blown filters was higher than that of uncharged media. Based on performance efficiency, melt-blown filters are more effective high efficiency particulate air filters than glass fiber media. Copyright

Formaldehyde and carbon dioxide air concentrations and their relationship with indoor environmental factors in daycare centers

ABSTRACT The aim of this study was to measure the air concentrations of carbon dioxide (CO2) and formaldehyde (HCHO) in daycare centers to determine relevant influencing factors, including temperature, relative humidity (RH), type of facility, number of children, type of ventilation system, ventilation time, and air cleaning system. The authors measured HCHO, CO2, temperature, and RH in the center of classrooms in 289 daycare centers. Spearman’s correlation and Mann–Whitney analyses were used to examine the relationships and differences in HCHO and CO2 for varying temperatures, RH values, and categorical indoor environmental factors. There were no significant differences in the HCHO and CO2 air concentrations with varying numbers of children, ventilation times, or ventilation and air cleaning system types. However, both the HCHO and CO2 air concentrations were significantly different for varying RH values, which were divided into five categories (p < 0.001). Only the HCHO air concentrations were significantly different for varying temperatures, which were divided into five categories (p < 0.001). Significant correlations were found between HCHO air concentrations and the temperature (r = 0.35, p < 0.0001), RH (r = 0.51, p < 0.0001), and CO2 (r = 0.36, p < 0.0001). The study results support maintaining an appropriate temperature and RH range for reducing airborne HCHO in daycare centers. Further research is needed to elucidate the precise mechanisms responsible for the relationships observed in this study. Implications: Data from 289 daycare centers in Seoul, South Korea, indicate that HCHO concentrations show a positive correlation with indoor temperature and relative humidity. This indicates that keeping temperatures low will help keep HCHO concentrations low, by both a direct and an indirect effect, since low temperatures also cause low relative humidity.