Hong-shik Shim

Low-Power Flexible Organic Light-Emitting Diode Display Device

Demands in extending fl at panel approaches to attain ultra-thin fl exible displays, which are lightweight, portable, and unbreakable for head-up displays, security identifi cation documents, conformable products, and electronic papers are ever increasing. [ 1‐3 ] A typical fl exible display comprises two major parts: i) driving circuitry to switch and address the display device, and ii) a fl exible display device to display an image and enhance outdoor readability. Signifi cant progress has been made in achieving stable rollable or bendable driving circuitry based on flthin fi lm transistors (TFTs), such as oxide transistors based on gallium indium zinc oxide (GIZO) [ 4 ] or hafnium indium zinc oxide (HIZO), [ 5 ] low temperature poly-Si (LTPS) on a plastic substrate (polyimide), [ 6 ] nanotube and nanowire-based transistors, [ 2 , 7 , 8 ] and organic thin fi lm transistors (OTFTs). [ 9 ] On the other hand, challenges to integrate a fl exible display device to realize full-color, low power, and outdoor readability have still not been addressed. Liquid crystal displays (LCDs) are widely used to fabricate commercial displays, but their optical system to switch a light source (backlight unit or light-emitting diode (LED) through a red/ green/blue (RGB) color fi lter) consists of a constant thick layer of liquid crystal molecules aligned between electrodes, and two polarization fi lms having the axes of transmission perpendicular to each other. Bending a LCD causes liquid crystal molecules to deform. The light that passes through the deformed liquid crystal molecules and two surrounding polarizing fi lms with perpendicular polarization axes is distorted causing display malfunction. In comparison, OLEDs do not suffer from such bending malfunctions, which makes OLEDs strong candidates for integration with fl exible electronics to achieve fl exible color displays. Current-generation OLEDs can afford a high performance and fl exibility, but this technology requires a polarization (POL) fi lm to enhance the contrast ratio for outdoor readability, and glass encapsulation to protect the OLED from oxygen and water. The fragile nature of these components limits their utility in fl exible OLED display devices. An advanced material to overcome the fragile components is required to allow the fl exible properties. In order to achieve a highly fl exible OLED display device, the following characteristics are needed: i) a low temperature process to prevent deformation in plastic substrates, ii) a new optical architecture providing both fl exibility and high outdoor readability, iii) a thinner and lighter platform than for current OLED technologies that allows bending and folding, iv) mechanical and electrical stability during repetitive folding, and v) optical reliability without malfunction from an ambient environment, especially water and oxygen.

Full Color Tunable Photonic Crystal from Crystalline Colloidal Arrays with an Engineered Photonic Stop‐Band

An electrically tunable photonic crystal is developed utilizing crystalline colloidal arrays of high refractive index particles. Through modulation of the refractive index of the particle, and the applied electric field, both the bandwidth and position of the photonic bandgap could be tuned. Full color modulation with high optical quality is achieved, which paves a way to develop a novel reflective display.

Mechanically and optically reliable folding structure with a hyperelastic material for seamless foldable displays

We report a mechanically and optically robust folding structure to realize a foldable active matrix organic-light-emitting-diode (AMOLED) display without a visible crease at the junction. A nonlinear stress analysis, based on a finite element method, provided an optimized design. The folding-unfolding test on the structure exhibited negligible deterioration of the relative brightness at the junction of the individual panels up to 105 cycles at a folding radius of 1 mm, indicating highly reliable mechanical and optical tolerances. These results demonstrate the feasibility of seamless foldable AMOLED displays, with potentially important technical implications on fabricating large size flexible displays.

Spectral reflectance switching of colloidal photonic crystal structure composed of positively charged TiO2 nanoparticles

We report the tunable photonic crystal behavior of highly concentrated, mildly charged TiO2 nanoparticle colloids under external electric field. Reflectance intensity change at the certain photonic bandgap and its irreversible switching characteristics are observed and discussed. Through computer aided numerical analysis, gradient spacing between charged particles is predicted under electric field, which is well coincidence with experimental results. Also, we report the experimental evidence that the charged nanoparticle can play the role as a major charge carrier in non-aqueous liquid. Its short range moving and stacking on electrode cause the capacitive current flow and charge accumulation like ions in liquid state.

18.4: A New Seamless Foldable OLED Display Composed of Multi Display Panels

A new seamless foldable OLED display composed of multi display panels is proposed. To verify seamless viewing and robust folding-unfolding reliability, a 138 ppi resolution, 5.4″ diagonal size AM-OLED seamless foldable display prototype is fabricated.

Electrically tunable photonic crystals from long-range ordered crystalline arrays composed of copolymer colloids

Due to recent growing interest in mobile and e-book devices, new demand for a display with excellent outdoor readability, low power consumption, and reduced eye fatigue has led to research on reflective displays. The crystalline colloidal arrays (CCAs) composed of monodisperse copolymer colloids, investigated in this study, offer great potential for a tunable photonic crystal to be applied to the display technology, owing to its high reflectance and colour purity, as well as to the precise controllability of the photonic colour in a full visible regime. With the help of the manipulability of the particle size and the surface charge, structural colour with improved viewing angle was produced by mixing colloids with different particle sizes. In addition, the stop-band tuning mechanism under the electric field was systematically investigated.

Stability enhancement of an electrically tunable colloidal photonic crystal using modified electrodes with a large electrochemical potential window

The color tuning behavior and switching stability of an electrically tunable colloidal photonic crystal system were studied with particular focus on the electrochemical aspects. Photonic color tuning of the colloidal arrays composed of monodisperse particles dispersed in water was achieved using external electric field through lattice constant manipulation. However, the number of effective color tuning cycle was limited due to generation of unwanted ions by electrolysis of the water medium during electrical switching. By introducing larger electrochemical potential window electrodes, such as conductive diamond-like carbon or boron-doped diamond, the switching stability was appreciably enhanced through reducing the number of ions generated.

43.2: Mutual Capacitance Touch Screen Integrated into Thin Film Encapsulated Active-Matrix OLED

A thin and high performance input/output device consisting of capacitive touch sensors integrated on thin film encapsulated AMOLED is described. Internal electric field distribution and capacitance change trend was simulated to find and prove the optimal structure including touch input and display output units. To verify cross-talk free operation of touch sensors on thin film encapsulated AMOLED, 4 inch diagonal size display-TSP prototype was fabricated.

P-214: Ultra Thin-Film Encapsulation for AMOLED Displays

A 5.4-inch AMOLED display was prepared using the combination of ultra thin film encapsulation steps with alternative organic and inorganic hybrid multi-layers. Organic layers for smoothing and improved adhesion were prepared by polyurea condensation with vapor deposition polymerization. Al2O3 inorganic layers were sequentially deposited on organic layers by sputtering. All processes were performed at room temperature. After optimization of the organic and inorganic layer deposition process, device operating lifetime performance was over 85%, as compared with glass encapsulation, and the transmittance of thin film multilayered structure was over 90% in the visible region.

36.4: A Novel Seamless Tiling Technology for High Resolution OLED Displays

A novel seamless tiling technology for high resolution OLED displays is described. This technology is mainly based on geometric arrangement of each pixels and optical path control of OLED displays. Computer simulations have been used to find and confirm the best conditions for seamless OLED displays. A 2 × 1 tiled, 72ppi resolution, 8″ diagonal size AM-OLED seamless tiled display prototype was fabricated.