Kwan-young Han

Origin of Leakage Paths Driven by Electric Fields in Al‐Doped TiO2 Films

The growth of leakage current paths in Al-doped TiO2 (ATO) films is observed by in situ TEM under negative bias stress. Through systematic HAADF-STEM, STEM-EDS, and STEM-EELS studies, it is confirmed that the electric field-induced growth of the Ru-doped TiO2 phase is the main reason for the ATO films negative leakage.

Curing Behavior and Viscoelasticity of Dual-Curable Adhesives Based on High-Reactivity Azo Initiator

We have investigated the curing behavior of dual-curable acrylic resin to solve problems associated with curing of adhesives in shaded areas during display manufacture. A low-temperature curing-type thermal initiator, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), with a 30°C half-life decomposition temperature was used in the investigation. Dual-curable adhesives were prepared according to the thermal initiator content and ultraviolet (UV) radiation dose. The effects of thermal initiator and UV irradiation on the curing behavior and viscoelasticity were investigated. Using Fourier-transform infrared spectroscopy and gel-fraction analysis, an evaluation was carried out to determine the degree of curing after dual UV/thermal curing. In addition, the real-time curing behavior was evaluated using thermogravimetric analysis, differential scanning calorimetry, and a UV/advanced rheometric expansion system. A lift-off test was carried out to verify the effects of dual curing on adhesion performance. Application of UV irradiation before thermal curing suppressed the thermal curing efficiency. Also, the network structure formed after dual curing with low UV dose showed higher crosslinking density. Therefore, the thermal initiator radical effectively influenced uncured areas with low curing temperature and initiator content without causing problems in UV-curable zones.

High-Linearity In-Pixel Thermal Sensor Using Low-Temperature Poly-Si Thin-Film Transistors

A novel highly linear thermal sensing scheme with thin-film transistor (TFT) reuse in a pixel circuit is presented for accurately extracting thermal information of each pixel in a display panel. Since the proposed sensor reuses existing TFTs of display pixels, the sensor can be easily embedded on the pixel, resulting in high compatibility and low cost. High conversion linearity of the proposed sensor is achievable by detecting the voltage difference between two driving TFTs of adjacent pixels operating at unequal current densities; this is based on experimental concept that the I-V transfer characteristic of an low-temperature polycrystalline-silicon (LTPS)-TFT in a subthreshold region can be modeled as an Arrhenius-like equation. Trimming methods for pixel-to-pixel spread on sensor inaccuracy are suggested, as well. The proposed thermal sensor was fabricated by using LTPS-TFT process to test the feasibility of its structure. With one-end-point calibration, the proposed thermal sensor achieves a measured inaccuracy of ±6 °C (±3σ) from 30 °C to 70 °C. After a spatial averaging with 16 sensors, the measured inaccuracy of maximum ±0.6 °C was achieved.

Viewing Distance-Based Perceived Error Control for Local Backlight Dimming

This paper presents an effective local dimming algorithm that preserves the perceived image quality consistently in the backlight dimmed images regardless of viewing distances. The proposed algorithm determines the clipped points of each LED block by limiting the maximum size of image area to be distorted, and guarantying the minimum image quality in terms of the peak signal-to-noise ratio. It also preserves the perceived image quality of the dimmed images by adjusting the size of area to be distorted depending on the viewing distances of users. Simulation results show that the proposed method improves the average PSNR and the average SSIM values of the dimmed images by 4.19-13.21 dB and 0.002-0.004, compared with the benchmark methods, for viewing distances of 2.5-6.5 m, respectively. The proposed method also maintains the image quality of the dimmed images regardless of the images characteristics, compared with the benchmark methods. In addition, it is confirmed that the proposed method achieves the higher power savings as the viewing distance increases. At the viewing distance of 6.5 m, although the image quality of the dimmed images are higher than that of the benchmark methods, the proposed method consumes 0.56% less power.

Transmission Electron Microscopy Specimen Preparation for Layer-area Graphene by a Direct Transfer Method

Graphene is a monolayer of carbon atoms arranged in a honeycomb lattice and is a basic building block for graphitic materials of all other dimensionalities. It can be wrapped up into zero-dimensional fullerenes, rolled into one-dimensional nanotubes or stacked into three-dimensional graphite. Graphene has unusual electrical, mechanical, and thermal properties, so it presents new opportunities in fundamental research and practical applications (Zhang et al., 2005; Geim & Novoselov, 2007; Geim, 2009). Recently, large-area synthesis methods for graphene have been advanced epitaxial growth on SiC (Brar et al., 2007; Qi et al., 2010) and chemical vapor deposition on metal substrates such as Ni (Dedkov et al., 2008) and Cu (Li et al., 2009). Particularly, Cu is a considerably attractive substrate because it can be produce layer-area graphene. Transmission electron microscopy (TEM) is a direct and re latively fast imaging tool ideally suited for suspended atomically thin membranes, so it has been successfully applied to study adsorbates on graphene and the atomic structure of graphene (Huang et al., 2011). To observe graphene by TEM, the graphene must transfer from metallic Cu substrates to a TEM grid. Standard transfer of layer graphene has been carried out using a polymer coating such as polymethyl methacrylate (PMMA) or polydimethylsiloxane as a temporary support during etching of the metal substrate to prevent tearing of the graphene (Reina et al., 2009). However, the standard transfer method using these polymers can contaminate and mechanically damage the graphene because it includes several wet chemical steps. Thus, a simple and gentle method is necessary for good TEM images of graphene. Direct transfer method doesn’t include polymer coating process. So it is expected simple and effective method to make graphene specimen by avoiding wet chemical steps (Regan, 2010).

Optimization of morphology of reflector for reflective LCDS

Abstract In this work, we propose a new surface profile of a reflector, which provides uniform reflectance within the whole viewing angular range. We show also the pararnetcrs to achieve uniform refleclance in the proper reflection range specified by uscr even if the incident angle of light is given arbitrarily. By using the Beckmanns scattering theory, we verify that the proposed surface. structure shows more enhanced rcflective property than that of CUSP.

Optically-controlled Alignment of Liquid Crystals on Alignment Layer (PWD) Containing Azo-group

Abstract To align liquid crystals on an alignment layer, the rubbing method is generally used. But it has some problems such as the generation of dust, and the difficulty of the quantitative control of rubbing intensity. To overcome these problems, we developed new photo-active mixture of w-dye (see the Fig. 1(a)) and PVA which can be applied as an alignment material for liquid crystal display (LCD). Using this polymer, we made cells and observed properties of a photo-alignment layer and LC alignment. From these results, we discussed the mechanism of LC and polymer alignment by UV irradiation in photo-alignment layer. We show that this new alignment material may be used in commercial LCDs.