• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.6
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• pp.1-6
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• 2011

A transparent oxide thin film transistors (Transparent Oxide-TFT) have been fabricated by RF magnetron sputtering at room temperature using amorphous indium zinc oxide (a-IZO) as both of active channel and source/drain, gate electrodes and co-sputtered $HfO_2-Al_2O_3$ (HfAIO) as gate dielectric. In spite of its high dielectric constant > 20), $HfO_2$ has some drawbacks including high leakage current and rough surface morphologies originated from small energy band gap (5.31eV) and microcrystalline structure. In this work, the incorporation of $Al_2O_3$ into $HfO_2$ was obtained by co-sputtering of $HfO_2$ and $Al_2O_3$ without any intentional substrate heating and its structural and electrical properties were investigated by x-ray diffraction (XRD), atomic force microscopy (AFM) and spectroscopic ellipsometer (SE) analyses. The XRD studies confirmed that the microcrystalline structures of $HfO_2$ were transformed to amorphous structures of HfAIO. By AFM analysis, HfAIO films (0.490nm) were considerably smoother than $HfO_2$ films (2.979nm) due to their amorphous structure. The energy band gap ($E_g$) deduced by spectroscopic ellipsometer was increased from 5.17eV ($HfO_2$) to 5.42eV (HfAIO). The electrical performances of TFTs which are made of well-controlled active/electrode IZO materials and co-sputtered HfAIO dielectric material, exhibited a field effect mobility of more than $10cm^2/V{\cdot}s$, a threshold voltage of ~2 V, an $I_{on/off}$ ratio of > $10^5$, and a max on-current of > 2 mA.

• Korean Journal of Environmental Agriculture
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• v.34 no.1
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• pp.6-13
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• 2015

BACKGROUND: Most of the tailings have been left without any management in abandoned metalliferous mines and have become the main source of heavy metal contamination for agricultural soils and crops in the these areas. METHODS AND RESULTS: This experiment was carried out to investigate the assessment of the heavy metal contamination in paddy soils located on downstream of the closed metalliferous mine. The average total concentrations of cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn), and arsenic (As) in paddy soils were 8.88, 56.7, 809, 754, and 37.9 mg/kg, respectively. Specially, the average concentrations of Cd, Pb and Zn were higher than those of warning criteria for soil contamination(4 mg/kg for Cd, 200 mg/kg for Pb, and 300 mg/kg for Zn) in agricultural soil established by Soil Environmental Conservation Act in Korea. The proportions of 0.1 M HCl extractable Cd, Cu, Pb, Zn, and As concentration to total concentration of these heavy metals in paddy soils were 27.7, 21.3, 35.1, 13.8 and 10.5%, respectively. The pollution index of these five metals in paddy soils ranged from 0.42 to 11.92. Also, the enrichment factor (EFc) of heavy metals in paddy soils were in the order as Cd>Pb>Zn>Cu>As, and the enrichment factor in paddy soil varied considerably among the sampling sites. The geoaccumulation index (Igeo) of heavy metals in soils were in the order as Cd>Pb>Zn>Cu>As, specially, the average geoaccumulation index of Cd, Pb, and Zn (Igeo 2.49~3.10) were relatively higher than that of other metals in paddy soils. CONCLUSION: Based on the pollution index, enrichment factor, and geoaccumulation index for heavy metal in paddy soils located on downstream of closed metalliferous mine, the main contaminants are mine waste materials and mine drainage including mine activity.