Sunkook Kim

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.

A Highly Sensitive Capacitive Touch Sensor Integrated on a Thin-Film-Encapsulated Active-Matrix OLED for Ultrathin Displays

This paper presents ultrathin and highly sensitive input/output devices consisting of a capacitive touch sensor (Cap-TSP) integrated on thin-film-encapsulated active-matrix organic light-emitting diodes (OLEDs). The optimal structure of the electrically noise-free capacitive touch sensor, which is assembled on a thin-film-encapsulated active-matrix OLED (AMOLED) display, is obtained by investigating the internal electrical field distribution and capacitance change based on the Q3D Extractor model. Electrostatic simulations have verified malfunction-free electrical signals for 4-in diagonal-sized capacitive touch sensors on AMOLEDs possessing a 100-μm-thick optically clear adhesive (OCA, εr = 1.4) layer. The prototype OLED platform using the capacitive touch sensors exhibits an overall thickness of 1.2 mm, which is the lowest thickness for commercially available OLED platforms.

Fully transparent pixel circuits driven by random network carbon nanotube transistor circuitry

Optically transparent and mechanically flexible thin-film transistors have recently attracted attention for next generation transparent display technologies. Driving and switching transistors for transparent displays have challenging requirements such as high optical transparency, large-scale integration, suitable drive current (I(on)) in the microampere range, high on/off current ratio (I(on)/I(off)), high field-effect mobility, and uniform threshold voltage (V(th)). In this study, we demonstrate fully transparent high-performance and high-yield thin-film transistors based on random growth of a single-walled carbon nanotube (SWNT) network that are easy to fabricate. High-performance SWNT-TFTs exhibit optical transmission of 80% in visible wavelength, I(on)/I(off) higher than 10(3), and a high yield with reproducible electrical characteristics.

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 105u2002cycles 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.

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.

Capacitance-voltage modeling of metal-ferroelectric-semiconductor capacitors based on epitaxial oxide heterostructures

We report a quantitative investigation on the capacitance-voltage (C-V) modeling of metal-ferroelectric-semiconductor epitaxial heterostructures based on a theoretical model. Within the carrier concentration between 1017 and 1021u2002cm−3, calculated C-V curves were consistent with measurements exhibiting from a significant asymmetry to a typical butterfly shape resembling that of a metal-ferroelectric-metal capacitor. The behavior of the C-V curves can be understood by the width of the depletion region and the extent of the depolarization field. These results suggest that quantitative understanding on the electrical behavior of oxide heterostructures is possible with C-V measurements with potentially important implications on their device applications.

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.

Shot Noise Thermometry for Thermal Characterization of Templated Carbon Nanotubes

A carbon nanotube (CNT) thermometer that operates on the principles of electrical shot noise is reported. Shot noise thermometry is a self-calibrating measurement technique that relates statistical fluctuations in dc current across a device to temperature. A structure consisting of vertical, top, and bottom-contacted single-walled carbon nanotubes in a porous anodic alumina template was fabricated and used to measure shot noise. Frequencies between 60 and 100 kHz were observed to preclude significant influence from Vf noise, which does not contain thermally relevant information. Because isothermal models do not accurately reproduce the observed noise trends, a self-heating shot noise model has been developed and applied to experimental data to determine the thermal resistance of a CNT device consisting of an array of vertical single-walled CNTs supported in a porous anodic alumina template. The thermal surface resistance at the nanotube-dielectric interface is found to be 1.5 × 108 K/W, which is consistent with measurements by other techniques.

Current on/off ratio enhancement through the electrical burning process in ambient with/without oxygen for the generation of high-performance aligned single-walled carbon nanotube field effect transistors

We present characteristics of the electrical burning process with/without oxygen-ambient for parallel aligned single-walled carbon nanotube field effect transistors (SWNT-FETs). High selectivity of metallic and semiconducting nanotubes is demonstrated by an electrical burning process through partial etching of the atomic layer deposited Al2O3 layer beneath the gate electrodes. Metallic nanotubes exposed to oxygen show electrical breakdown during the burning process, resulting in the SWNT-FETs having excellent performance. Specifically, 100u2002μm source/drain width p-type aligned SWNT-FETs through electrical burning with local oxidation show high Ion/Ioff ratios (>103), 10u2002μS at a drain bias of −1 V and −100u2002μA at a reverse gate bias of −8 V.