Jun-Hong Park

Suppressed Instability of a-IGZO Thin-Film Transistors Under Negative Bias Illumination Stress Using the Distributed Bragg Reflectors

We suggest functional passivation layers in the form of a distributed Bragg reflector (DBR) composed of ZnS and LiF for transparent thin-film transistors (TFTs) to improve the stability under negative bias illumination stress (NBIS). The luminous transmittance of the DBR was 82.0% when the number of dyads was 3.5, and the thicknesses of ZnS and LiF were 42 and 85 nm, respectively. We applied the DBR to TFTs based on amorphous indium-gallium-zinc oxide without the degradation of electrical performance, such as the mobility, ON-OFF ratio, subthreshold swing, and VON. The luminous transmittance of the TFT with the DBR was measured as 71.6%. ΔVON of the TFT with the DBR was reduced to -1.119 V compared with that of the reference TFT, which is -3.261 V when a 1.25 MV/cm electric field was applied, and white light was illuminated during 3000 s. This confirms that the functional passivation layers suggested, in this paper, provide a solution to suppress the instability of TFTs in the NBIS and enhance the optical transmittance of transparent displays.

Low-Resistive High-Work-Function Gate Electrode for Transparent a-IGZO TFTs

Highly transparent and low-resistive multilayered gate electrodes, MoO3/indium-tin oxide (ITO)/Ag/ ZnS (MIAZ) playing as the high-work-function layer, the nonreactive interface layer, the lateral conduction layer, and the index-matching layer, respectively, have been investigated for the application to the transparent oxide thin-film transistors (TFTs). The transmittance of the optimized MIAZ electrode is 92.46% and the sheet resistance is 7.77 Ω/□. The top gate InGaZnO TFT with this gate electrode shows the mobility of 11.57 cm2/(V · s) and positive Vth of 0.210 V compared with that with single ITO gate electrode of which Vth is -0.086 V.

Characterization of Clay Minerals in Ranch Pasture

This study deals with the distribution of the clay minerals separated from clay fractions of ranch pastures in Korea and their chemical and mineralogical properties. Crystalline phases of the clay minerals were identified by powder X-ray diffraction (XRD) pattern and FT-IR spectra, and their relative chemical compositions were also analyzed by X-ray flourescence spectrometry (XRF). Primary minerals consisted mainly of quartz and mica and chlorite and kaolinite along with a trace of swelling micas were identified as secondary clay minerals. However, the relative content of these clay minerals was different with the locations, which led to significant effects on physical and chemical properties of soils like inorganic elemental composition. In particular, SiO₂ content was higher in Gochang ranch pasture than in other ranch pasture. Infrared (IR) spectra did not indicate any significant differences in organic functional groups among the locations. This study clearly showed that ranch pastures had different relative content of clay minerals and chemical properties depending on the location and consequently that those properties are worthy to be taken into account for soil amendment.

Low-Temperature Fabrication of Robust, Transparent, and Flexible Thin-Film Transistors with a Nanolaminated Insulator

The lack of reliable, transparent, and flexible electrodes and insulators for applications in thin-film transistors (TFTs) makes it difficult to commercialize transparent, flexible TFTs (TF-TFTs). More specifically, conventional high process temperatures and the brittleness of these elements have been hurdles in developing flexible substrates vulnerable to heat. Here, we propose electrode and insulator fabrication techniques considering process temperature, transmittance, flexibility, and environmental stability. A transparent and flexible indium tin oxide (ITO)/Ag/ITO (IAI) electrode and an Al2O3/MgO (AM)-laminated insulator were optimized at the low temperature of 70 °C for the fabrication of TF-TFTs on a polyethylene terephthalate (PET) substrate. The optimized IAI electrode with a sheet resistance of 7 Ω/sq exhibited the luminous transmittance of 85.17% and maintained its electrical conductivity after exposure to damp heat conditions because of an environmentally stable ITO capping layer. In addition, the electrical conductivity of IAI was maintained after 10 000 bending cycles with a tensile strain of 3% because of the ductile Ag film. In the metal/insulator/metal structure, the insulating and mechanical properties of the optimized AM-laminated film deposited at 70 °C were significantly improved because of the highly dense nanolaminate system, compared to those of the Al2O3 film deposited at 70 °C. In addition, the amorphous indium-gallium-zinc oxide (a-IGZO) was used as the active channel for TF-TFTs because of its excellent chemical stability. In the environmental stability test, the ITO, a-IGZO, and AM-laminated films showed the excellent environmental stability. Therefore, our IGZO-based TFT with IAI electrodes and the 70 °C AM-laminated insulator was fabricated to evaluate robustness, transparency, flexibility, and process temperature, resulting in transfer characteristics comparable to those of an IGZO-based TFT with a 150 °C Al2O3 insulator.

Comparison of the Surface Chemical Properties of Plastic Film House, Upland, and Orchard Soils in Gyeongbuk Province

The objectives of this study were to evaluate the soil fertility about plastic film house, upland, and orchard in Gyeongbuk Province, Korea. The surface chemical properties of soil samples were investigated every 4 year from 2000 year at upland, 2001 year at orchard, and 2002 year at plastic film house. During 12 year’s monitoring, mean soil pH was increased by 0.7 and 0.8 pH unit from pH 5.7 in upland and orchard, respectively, 0.5 pH unit from pH 6.5 in plastic film house. About 50% of all the field samples occupied within the recommended pH range (pH 6-7). Although soil organic matter (SOM) was gradually increased by about 10 g ㎏ -1 for 12 years, 40% of orchard, 49% of plastic film house, and 77% of upland soil samples were still below the 3% SOM. The mean concentration of available phosphate for 12 years in upland, orchard, and plastic film house were 530, 600, and 760 mg ㎏ -1 , respectively. The relative frequencies exceeding the recommended available phosphate range (300-550 ㎎ ㎏ -1 ) were 43%, 53%, and 66% at upland, orchard, and plastic film house soils, respectively. NH₄OAc exchangeable K⁺ of upland, orchard, and plastic film house in the last soil test were 0.8, 0.9, and 1.6 cmolc ㎏ -1 , respectively. The relative frequencies above the recommended K level were 56% and 70% of orchard and plastic film house soil samples, respectively. The levels of crop nutrients except exchangeable Ca and Mg in upland soil were tended to increase gradually in the three fields. Exchangeable Mg, EC, available phosphate, organic matter and soil pH could be used as principle components to differentiate the chemical properties of three land fields. This analysis revealed that the soil fertility was affected by cropping method and field management, although additional research is needed to assess the importance of management on soil chemical properties and many fields indicate an opportunity for improvement in fertilizer management.

Effect of Mixed Treatment of Urea Fertilizer and Zeolite on Nitrous Oxide and Ammonia Emission in Upland Soil

Ammonia loss from urea significantly hinders efficient use of urea in agriculture. The level of nitrous oxide (N₂O) a long-lived greenhouse gas in atmosphere has increased mainly due to anthropogenic source, especially application of nitrogen fertilizers. There are reports in the literature showing that the addition of zeolite to N sources can improve the nitrogen use efficiency. This study was conducted to evaluate nitrous oxide (N₂O) and ammonia (NH₃) emission by mixed treatment of urea and zeolite in upland crop field. Urea fertilizer and zeolite were applied at different rates to study their effect on N₂O emission during red pepper cultivation in upland soils. The N₂O gas was collected by static closed chamber method and measured by gas chromatography. Ammonia concentration was analyzed by closed-dynamic air flow system method. The total N₂O flux increased in proportion to the level of N application. Emission of N₂O from the field increased from the plots applied with urea-zeolite mixture compared to urea alone. But urea-zeolite mixture treatment reduced about 30% of NH₃-N volatilization amounts. These results showed that the application of urea and zeolite mixture had a positive influence on reduction of NH3 volatilization, but led to the increase in N₂O emission in upland soils.

Effects of Soil Types on Methane Gas Emission in Paddy During Rice Cultivation

Anaerobic decomposition of organic materials in flooded rice fields produces methane () gas, which escapes to the atmosphere primarily by transport through organs of the rice plants such as arenchyma etc., Although the annual amount of methane emitted from a given area is influenced by cultivation periods of rice and organic/inorganic amendments etc., soil type also affects methane emission from paddy soil during a rice cultivation. A field experiment was conducted to evaluate effects of soil type on emission in two paddy soils. One is a red-yellow soil classified as a Hwadong series (fine, mixed, mesic family of Aquic Hapludalfs), and the other is a gley soil classified as a Shinheung series (fine loamy, mixed, nonacid, mesic family of Aeric Fluvaquentic Endoaquepts). During a flooded periods, redox potentials of red-yellow soil were significantly higher than gley soil. emission in red-yellow soil () was lower than that in gley soil (). In the condition of different soil types, emissions were mainly influenced by the content of total free metal oxides in paddy soil. The results strongly imply that iron- or manganese-oxides of well ordered crystalline forms in soil such as goethite and hematite influenced on a emission, which is crucial role as a oxidizers in paddy soil during a rice cultivation.

Assessing Changes in Selected Soil Chemical Properties of Rice Paddy Fields in Gyeongbuk Province

Received: February 2, 2017 Revised: April 26, 2017 Accepted: May 26, 2017 This study was conducted with the data of monitoring on soil chemical properties of rice paddy soils in Gyeongbuk Province. The selected soil chemical properties were analyzed every 4 year from 1999 to 2015. The soil pH measured in 2015 was higher than pH 6.0, which was 0.3-0.4 pH unit higher than data until 2007 survey year. The mean content of organic matter was greater than 24 g kg-1 since 2003, but 35% of soil samples remained below the recommended level (20-30 g kg-1) in 2015. The mean concentration of available phosphate was maintained at 40 mg kg-1 higher than the upper recommendation level (80-120 mg kg-1), and more than 40% of paddy soils tested were found to have less than the recommendation level during the survey period. The exchangeable K concentration ranged from 0.25 to 0.39 cmolc kg -1. Exchangeable Ca showed an average at the optimum range (5.0-6.0 cmolc kg -1) during the monitoring period. Exchangeable Mg decreased linearly (0.02 cmolc kg -1 year-1) from 1.55 cmolc kg -1 as of 1999 to below the lower level of the recommendation range (1.5-2.0 cmolc kg -1). The amount of available SiO2 was increased significantly from 2011 to over the recommendation level (≥157 mg kg-1). It was revealed that the soil chemical properties of rice paddy fields was influenced by topology, soil texture, type and region as result of principal component analysis or cluster analysis. Therefore, an assessment on chemical properties of rice paddy soils should be performed to consider various soil physical conditions and agronomic practices such as fertilization, cropping system, and so on. Because of the high variability of nutrient levels across Gyeongbuk Province, nutrient management based on soil fertility test is required by respective farm land unit.

Soil Physico-chemical Properties by Land Use of Anthropogenic Soils Dredged from River Basins

This study was conducted to analyze soil physico-chemical properties of agricultural land composed from the river-bed sediments. We investigated the changes of soil physico-chemical properties at 30 different sampling sites containing paddy, upland and plastic film house from 2012 to 2015. pH, exchangeable calcium and magnesium decreased gradually in paddy soils during the four years, whereas the available P₂O 5 , exchangeable Ca, Mg and EC increased in upland and plastic film house soil. For the soil physical properties, bulk density and hardness of topsoil were 1.47 g cm -3 and 21.5 mm and those of subsoil were 1.71 g cm -3 and 25.7 mm in paddy soils. In upland soils, bulk density and hardness of topsoil were 1.48 g cm -3 and 15.9 mm and those of subsoil were 1.55 g cm -3 and 16.9 mm. In plastic film house soils, bulk density and hardness of topsoil were 1.42 g cm -3 and 14.4 mm and those of subsoil were 1.40 g cm -3 and 18.5 mm, respectively. The penetration hardness was higher than 3 MPa below soil depth 20 cm, and it is impossible to measure below soil depth 50 cm. As these results, in agricultural anthropogenic soils dredged from river basins, the pH, amount of organic matter and exchangeable cations decreased and soil physical properties also deteriorated with time. Therefore, it is needed to apply more organic matters and suitable amount of fertilizer and improve the soil physical properties by cultivating green manure crops, deep tillage, and reversal of deep soils.

Assessing Soil Fertility Status of Edible Wild Plants Fields in Ulleung Island

The perennial edible wild plants such as Aster glehnii, Solidago virgaurea subsp. gigantean, Allium ochotense, Athyrium acutipinnulum, Aruncus dioicus var. kamtschaticus and Codonopsis lanceolata have cultivated as the main income crops introduced into the fields about 30 years ago in Ulleung island. Soil samples were collected from 190 fields and assessed the effects of management practices on soil chemical properties at wild edible plant fields under no-till system. The strong acidic soils of pH 5.4 or less were detected in 45% of the soil samples. The level of soil organic matter was being held at mean 63±28 g kg -1 , 2.7 times higher than upland soils in Korea. Available phosphate and exchangeable potassium showed more than recommended levels of upland crops as 680±489 mg kg -1 and 1.94±1.7 cmolc kg -1 , respectively. The fields of Solidago and Aster showing strong soil acidity and high level of available phosphate and water soluble NO₃ - were distinguished from other crops in analysis of variance and principal component analysis of soil chemicals. These results suggested that high frequency of acidic soil and high levels of available P₂O 5 , exchangeable K₂O and water soluble NO₃ - were accompanied with the use of urea and NPK-fertilizer based on nitrogen in the field. However, further research is needed to understand the appropriate management of fertilization and the prevention of soil acidification for wild edible plants.