Young Tea Chun

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.

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.

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.

High optical and switching performance electrochromic devices based on a zinc oxide nanowire with poly(methyl methacrylate) gel electrolytes

High performance electrochromic devices have been fabricated and demonstrated utilizing a solid polymer electrolyte and zinc oxide (ZnO) nanowire (NW) array counter electrode. The poly(methyl methacrylate) based polymer electrolyte was spin coated upon hydrothermally grown ZnO NW array counter electrodes, while electron beam evaporated NiOx thin films formed the working electrodes. Excellent optical contrast and switching speeds were observed in the fabricated devices with active areas of 2 cm2, exhibiting an optical contrast of 73.11% at the wavelength of 470 nm, combined with a fast switching time of 0.2 s and 0.4 s for bleaching and coloration, respectively.

High performance non-volatile ferroelectric copolymer memory based on a ZnO nanowire transistor fabricated on a transparent substrate

A high performance ferroelectric non-volatile memory device based on a top-gate ZnO nanowire (NW) transistor fabricated on a glass substrate is demonstrated. The ZnO NW channel was spin-coated with a poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) layer acting as a top-gate dielectric without buffer layer. Electrical conductance modulation and memory hysteresis are achieved by a gate electric field induced reversible electrical polarization switching of the P(VDF-TrFE) thin film. Furthermore, the fabricated device exhibits a memory window of ∼16.5 V, a high drain current on/off ratio of ∼105, a gate leakage current below ∼300 pA, and excellent retention characteristics for over 104 s.

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.

Broadband MoS2 Field-Effect Phototransistors: Ultrasensitive Visible-Light Photoresponse and Negative Infrared Photoresponse.

Inverse photoresponse is discovered from phototransistors based on molybdenum disulfide (MoS2 ). The devices are capable of detecting photons with energy below the bandgap of MoS2 . Under the illumination of near-infrared (NIR) light at 980 and 1550 nm, negative photoresponses with short response time (50 ms) are observed for the first time. Upon visible-light illumination, the phototransistors exhibit positive photoresponse with ultrahigh responsivity on the order of 104 -105 A W-1 owing to the photogating effect and charge trapping mechanism. Besides, the phototransistors can detect a weak visible-light signal with effective optical power as low as 17 picowatts (pW). A thermally induced photoresponse mechanism, the bolometric effect, is proposed as the cause of the negative photocurrent in the NIR regime. The thermal energy of the NIR radiation is transferred to the MoS2 crystal lattice, inducing lattice heating and resistance increase. This model is experimentally confirmed by low-temperature electrical measurements. The bolometric coefficient calculated from the measured transport current change with temperature is -33 nA K-1 . These findings offer a new approach to develop sub-bandgap photodetectors and other novel optoelectronic devices based on 2D layered materials.

P-16: Integration of the 4.5″ Active Matrix Organic Light-emitting Display with Organic Transistors

We developed an active matrix organic light-emitting display(OLED) on a glass using two organic thin-film transistors(OTFTs) and a capacitor in a pixel. The OTFTs has bottom contact structure with a unique gate insulator and pentacene for the active layer. The width and length of the switching OTFT is 500 μm and 10 μm respectively and the driving OTFT has 900 μm channel width with the same channel length. The characteristics of the OTFTs were examined by test cells around display area and generated images on the panel. The mobility was 0.3 cm2V−1S−1 and the current on/off ratio was 106. The uniformity and stability were confirmed through still and moving images on the panel. The organic light-emitting layers were fabricated by shadow mask process and color fluorescence materials were used for the emitting layers. The resolution of the panel is 64×RGB×64 in 4.5 inch diagonal and the aperture ratio was 25%.

Defect-mediated modulation of optical properties in vertically aligned ZnO nanowires via substrate-assisted Ga incorporation

We report the defect-mediated modulation of optical properties in vertically aligned ZnO nanowires via a substrate-assisted Ga incorporation method. We find that Ga atoms were incorporated into a ZnO lattice via the diffusion of liquid Ga droplets from a GaAs substrate in which as-grown ZnO nanowires were placed face down on the GaAs substrate and annealed at 650 °C. Based on structural and compositional characterization, it was confirmed that the substrate-assisted incorporation of Ga can induce a high defect density in vertically aligned ZnO nanowires grown on a Si substrate. In addition, distinct differences in optical properties between as-grown and Ga-incorporated ZnO nanowires were found and discussed in terms of defect-mediated modifications of energy band states, which were associated with the generation and recombination of photoexcited carriers. Furthermore, it was clearly observed that for Ga-incorporated ZnO nanowires, the photocurrent rise and decay processes were slower and the photocurrents under UV illumination were significantly higher compared with as-grown nanowires.