Chang-Dong Kim

New Depletion-Mode IGZO TFT Shift Register

A new shift register employing bottom-gate In-Ga-Zn-O thin-film transistors (IGZO TFTs) was proposed and fabricated. Depletion-mode IGZO TFTs were successfully turned off by employing two low-voltage-level signals. The IGZO shift register exhibited a high-voltage output pulse without any distortion and a maximum clock frequency of 417 kHz. The proposed shift register would be an important building block for a depletion-mode oxide TFT display.

Highly Flexible AM-OLED Display With Integrated Gate Driver Using Amorphous Silicon TFT on Ultrathin Metal Foil

This paper introduces the technology behind developing of flexible AM-OLED displays with improved color and reduced bending radius. Developing a-Si TFT fabrication technology using 80-μm ultrathin stainless steel foil as the substrate and integrating driver electronic in the display panel, we were able to demonstrate a full-color AM-OLED displayed in a curvature of less than 5 cm bending radius. Total panel thickness of 0.30 mm, brightness of 100 cd/m2 and color reproducibility of 63% were achieved.

A Depletion-Mode a-IGZO TFT Shift Register With a Single Low-Voltage-Level Power Signal

We proposed and fabricated a new depletion-mode amorphous indium-gallium-zinc-oxide thin-film-transistor (a-IGZO TFT) shift register. Although only one low-voltage-level power signal (VGL) rather than widely used two ones was employed, the depletion-mode a-IGZO TFTs in the proposed shift register were turned off completely due to a series-connected two-transistor structure. The proposed shift register exhibited successfully a high-voltage output pulse. The power consumption of the shift register with ten stages is 1.67 mW at the high-voltage-level power signal of 20 V, the VGL of -5 V, and the clock frequency of 13.9 kHz.

a-Si:H Thin-Film Transistor-Driven Flexible Color E-Paper Display on Flexible Substrates

A 14.3-in flexible color electronic-paper display with the highest resolution has been developed. This display uses an electrophoretic material between a-Si:H thin-film transistors (TFTs) on a metal foil and a color filter array (CFA) coated onto a plastic substrate, allowing it to recover its original shape after being bent and to produce color images. To make this new display possible, low-temperature processes ( <; 150°C) for TFT and CFA on flexible substrates have been developed, resulting in the minimization of panel deformation and the prevention of circuit structure change. Here, we also develop a U-type dual TFT structure and a quad-type CFA pattern suitable for this reflective-type display.

A Depletion-Mode In–Ga–Zn–O Thin-Film Transistor Shift Register Embedded With a Full-Swing Level Shifter

We proposed and fabricated the shift register embedded with a full-swing level shifter employing the depletion-mode In-Ga-Zn-O thin-film transistors (IGZO TFTs). In the level shifter, two clock signals with 180° out of phase and one start signal were employed to obtain a full-swing output. Also, the depletion-mode IGZO TFTs in the shift register were successfully turned off by employing two low-voltage-level signals. The level shifter and the shift register consist of six TFTs and one capacitor, and 11 TFTs, respectively. The depletion-mode IGZO TFT shift register embedded with a level shifter exhibited a high-voltage output pulse without any distortion. The power consumption is 2.13 mW at a VGH of 20 V, a VGL1 of -10 V, and a clock frequency of 12.5 kHz.

76.2: Development of Highly Stable a‐IGZO TFT with TiOx as a Passivation Layer for Active‐Matrix Display

Titanium oxide (TiOx) was employed for passivation layer of indium-gallium-zinc oxide (a-IGZO) TFTs. Molybdenum (Mo) and titanium (Ti) was used as a source-drain metal. It is demonstrated the titanium layer could be used as an etch stopper layer to protect the back channel of a-IGZO during Mo etching process and transformed into TiOx by the surface treatment using oxygen plasma. From device measurement, we have observed that Ion/Ioff ratio and mobility are ∼108 and 9 cm2 V−1 sec−1, respectively. AMLCD panel has been demonstrated to verify the device uniformity and performance.

A Novel Level Shifter Employing IGZO TFT

A new level shifter employing indium-gallium-zinc-oxide thin-film transistor (IGZO TFT) for a display panel was proposed and successfully fabricated. Two clock signals with 180° out of phase and a discharging TFT were employed to obtain a full-swing output. The IGZO level shifter has successfully exhibited a wide swing output from VDD to VSS without any additional power sources and input signals. The power consumption is 0.30 mW at a clock frequency of 12.5 kHz. The proposed level shifter with a depletion-mode device would be an important building block for an oxide TFT display.

Wearable 4‐in. QVGA full‐color‐video flexible AMOLEDs for rugged applications

— Work on the worlds first wrist-worn communications device built on a flexible, low-power-consumption full-color AMOLED using phosphorescent OLEDs is presented. The device offers the wearer the ability to see high-information-content video-rate information in a thin-and-rugged-form-factor 4-in. QVGA display, conformed around a human wrist.

3.1: A New AMOLED Pixel Compensating the Combination of n-Type TFT and Normal OLED Device

A new AMOLED pixel circuit was proposed to compensate for the mismatched combination of n-type TFT and normal bottom-emission OLED. The proposed pixel also compensates for the variation of TFT characteristics and I×R voltage rise in power line. 15-inch AMOLED panel employing reliable a-SPC TFT backplane and the proposed pixel has been developed.

A study of roll-printing technology for TFT-LCD fabrication

— Recently, potential breakthrough technologies for low-cost processing of TFT-LCDs and new process developments for flexible-display fabrication have been widely studied. A roll-printing process using etch-resist material as a replacement for photolithographic patterning was investigated. The characterization of the properties of patterns formed in roll printing, a method to fabricate cliche plates for fine patterns, and the design of a new formulation for resist printing ink is reported. The pattern position accuracy, which is one of the most important issues for the successful application of printing processes in display manufacturing was studied and how it can be improved by optimizing the blanket roll structure is explained. New design rules for the layout of the thin-film-transistor array was derived to improve the compatibility of roll printing. As a result, a prototype 15-in.-XGA TFT-LCD panel was fabricated by using printing processes to replace all the photolithographic patterning steps conventionally used.