Showing papers by "Jaehoon Park published in 2017"

Low-Concentration Indium Doping in Solution-Processed Zinc Oxide Films for Thin-Film Transistors.

Abstract: We investigated the influence of low-concentration indium (In) doping on the chemical and structural properties of solution-processed zinc oxide (ZnO) films and the electrical characteristics of bottom-gate/top-contact In-doped ZnO thin-film transistors (TFTs). The thermogravimetry and differential scanning calorimetry analysis results showed that thermal annealing at 400 °C for 40 min produces In-doped ZnO films. As the In content of ZnO films was increased from 1% to 9%, the metal-oxygen bonding increased from 5.56% to 71.33%, while the metal-hydroxyl bonding decreased from 72.03% to 9.63%. The X-ray diffraction peaks and field-emission scanning microscope images of the ZnO films with different In concentrations revealed a better crystalline quality and reduced grain size of the solution-processed ZnO thin films. The thickness of the In-doped ZnO films also increased when the In content was increased up to 5%; however, the thickness decreased on further increasing the In content. The field-effect mobility and on/off current ratio of In-doped ZnO TFTs were notably affected by any change in the In concentration. Considering the overall TFT performance, the optimal In doping concentration in the solution-processed ZnO semiconductor was determined to be 5% in this study. These results suggest that low-concentration In incorporation is crucial for modulating the morphological characteristics of solution-processed ZnO thin films and the TFT performance.

A 650 V Super-Junction MOSFET With Novel Hexagonal Structure for Superior Static Performance and High BV Resilience to Charge Imbalance: A TCAD Simulation Study

Abstract: A superjunction MOSFET (SJ-MOSFET) with a new fully close-packed hexagonal pattern for its superjunction (SJ) region is proposed. According to TCAD simulation, the proposed device can accommodate highly doped n-pillars with no significant degradation of its blocking voltage (BV), where its conventional counterpart, a SJ-MOSFET with a stripe-patterned SJ region is incapable of. In comparison with the conventional device, the proposed device shows dramatic reduction of ON-resistance down by 41% while keeping its BV of 650 V. The proposed device also shows superior BV resilience to charge imbalance than the conventional device.

Solution-Processed Gallium-Tin-Based Oxide Semiconductors for Thin-Film Transistors.

Abstract: We investigated the effects of gallium (Ga) and tin (Sn) compositions on the structural and chemical properties of Ga–Sn-mixed (Ga:Sn) oxide films and the electrical properties of Ga:Sn oxide thin-film transistors (TFTs). The thermogravimetric analysis results indicate that solution-processed oxide films can be produced via thermal annealing at 500 °C. The oxygen deficiency ratio in the Ga:Sn oxide film increased from 0.18 (Ga oxide) and 0.30 (Sn oxide) to 0.36, while the X-ray diffraction peaks corresponding to Sn oxide significantly reduced. The Ga:Sn oxide film exhibited smaller grains compared to the nanocrystalline Sn oxide film, while the Ga oxide film exhibited an amorphous morphology. We found that the electrical properties of TFTs significantly improve by mixing Ga and Sn. Here, the optimum weight ratio of the constituents in the mixture of Ga and Sn precursor sols was determined to be 1.0:0.9 (Ga precursor sol:Sn precursor sol) for application in the solution-processed Ga:Sn oxide TFTs. In addition, when the Ga(1.0):Sn(0.9) oxide film was thermally annealed at 900 °C, the field-effect mobility of the TFT was notably enhanced from 0.02 to 1.03 cm2/Vs. Therefore, the mixing concentration ratio and annealing temperature are crucial for the chemical and morphological properties of solution-processed Ga:Sn oxide films and for the TFT performance.

Temperature and molecular-weight dependences of acoustic behaviors of polystyrene studied using Brillouin spectroscopy

Abstract: The acoustic properties of three polystyrene polymers with different molecular weights were investigated as a function of temperature by using Brillouin light scattering. The longitudinal sound velocity showed a change in the slope, which depended on the molecular weight, at the glass transition temperature. The absorption coefficient exhibited a maximum above the glass transition temperature, and the maximum temperature became higher as the molecular weight was increased. Comparison with previous acoustic studies on polystyrene indicate that a substantial frequency dispersion caused by strong coupling between the longitudinal acoustic waves and the segmental motions exists in the high-temperature range.

Association Rule-based Predictive Model for Machine Failure in Industrial Internet of Things

Abstract: This paper proposes an association rule-based predictive model for machine failure in industrial Internet of things (IIoT), which can accurately predict the machine failure in real manufacturing environment by investigating the relationship between the cause and type of machine failure To develop the predictive model, we consider three major steps: 1) binarization, 2) rule creation, 3) visualization The binarization step translates item values in a dataset into one or zero, then the rule creation step creates association rules as IF-THEN structures using the Lattice model and Apriori algorithm Finally, the created rules are visualized in various ways for users' understanding An experimental implementation was conducted using R Studio version 332 The results show that the proposed predictive model realistically predicts machine failure based on association rules

Effect of crystallinity on acoustic behaviors of biocompatible silk studied by Brillouin spectroscopy

Abstract: Temperature dependences of thermal, thermogravimetric, and acoustic properties were investigated for the crystalline silk fibroin films crystallized by methanol exposure. The crystallization peak in the thermal flow at ~ 225 ◦ C, which was prominent in the amorphous silk film, disappeared in the crystalline silk film. The heat-treatment at ~ 100 ◦ C for 1 h reduced the weight by ~5.5% due to the release of water molecules. The formation of beta-sheets in the film did not have any substantial effect on the acoustic properties of the longitudinal acoustic mode in the crystalline film. However, the heat treatment of the methanol-exposed silk film induced clear anomalies in the acoustic mode behaviors in a specific temperature range between −20 ~ 30 ◦ C. The existence of water molecules has more profound effect than the crystallinity does on the acoustic properties of silk fibroin films.

Bias stress effects in pentacene thin-film transistors with poly(methyl methacrylate) gate insulator

Abstract: We demonstrated a bias stress effect on organic thin-film transistors (OTFTs) that causes device degradation, including a large shift in the threshold voltage and hysteresis in the transfer characteristics. Specifically, we analyzed the electrical characteristic variations in pentacene TFTs with a poly(methyl methacrylate) gate insulator under different bias stress conditions. We found that bias stress between the gate electrode and source/drain electrodes affects the charge transport properties, whereas bias stress between the source and drain electrodes influences the charge injection properties.