Young-gu Lee

42.4L: Late‐News Paper: 4 inch QVGA AMOLED Driven by the Threshold Voltage Controlled Amorphous GIZO (Ga2O3‐In2O3‐ZnO) TFT

We successfully fabricated GIZO (Ga2O3-In2O3-ZnO) TFTs with high mobility of 2.6 cm2/Vs and threshold voltage standard deviation of 0.7V which is comparable to that of a-Si TFTs. Because conventional 5 mask process and bottom gate TFT structure of back channel etch type with channel length of 5 μm is used, it is expected to be transferred to mass production line in near future. Also we report the dependency of threshold voltage on the post process after the back surface of GIZO is exposed and suggest the effective method for controlling the threshold voltage of amorphous GIZO TFTs. Finally we demonstrate 4 inch QVGA AMOLED display driven by GIZO TFTs.

Photopatternable quantum dots forming quasi-ordered arrays.

We have functionalized core-shell CdSe/ZnS quantum dots (QDs) with a photosensitive monolayer, rendering them solution processable and photopatternable. Upon exposure to ultraviolet radiation, films composed of this material were found to polymerize, forming interconnected arrays of QDs. The photoluminescence properties of the nanocrystal films increased with photocuring. The material was found to be suitable for spin casting and was used as the active layer in a green electroluminescent device. The electroluminescence efficiency of devices containing a photocured active layer was found to be largely enhanced when compared to devices containing nonphotocured active layers. The material also showed excellent adhesion to both organic and inorganic substrates because of the unique combination of a siloxane and a photopatternable layer as ligands. The pristine functionalized nanocrystals could easily be used for two-dimensional patterning on organic and inorganic substrates. The photopatternable quantum dots were uniformly dispersed into a photopolymerizable resin to fabricate QD embedded three-dimensional microstructures.

3.5: Invited Paper: Recent Progress in Large Sized & High Performance Organic TFT Array

Recently, we have developed 15.0 inch XGA organic TFT array and its LCD module, which might be world-largest array size and highest resolution in organic based device. This achievement is to be combined with several technical breakthroughs include new organic gate dielectric material, novel ohmic contact technique, and well-optimized process-architectures. Base on the newly developed organic gate dielectric with pentacene, we have obtained world-record field effect TFT mobilities in excess of 7cm2/Vsec and excellent on/off ratios as ∼106. For jumping up the OTFT research activities from laboratory scale to real production line, we have developed two key technologies. One is the new ohmic contact process with very common materials in the current LCD manufacturing such as ITO; the bottom contact structured OTFT with ITO source-drain electrode shows much the same performances as that with gold source-drain electrode. The other key technology to realize the large size organic device is that of optimizing the array structure to minimize the OTFT performance degradations. By combining these novel technologies, a 15.0″ XGA prototype LCD panel is fabricated and shows good display performance.

15.3: AMOLED Driven by Solution-Processed Oxide Semiconductor TFT

We report an AMOLED fabricated with a solution-processed indium zinc oxide (IZO) thin-film transistor (TFT) backplane. The TFT has a bottom gate structure with SiNx gate insulator, spin-coated IZO active layer, Mo source/drain electrode, and SiO2 passivation layer. The TFT exhibited the field effect mobility of 0.9 cm2/Vs, threshold voltage of 13.6 V, and high on/off current ratio of 1.8e7.

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.

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%.

Simulations of Electrical Characteristics of Multi-layer Organic Light Emitting Diode Devices with doped Emitting Layer

We have performed numerical simulations of the electrical characteristics for multi-layer organic light emitting diode devices with doped emitting layer using a commercial simulation program. In this paper, the basic structure consists of the ITO/NPB/:C545T(%)//LiF/Al, four devices that were composed of as the host and C545T as the green dopant with different concentration, were studied. As the result, the variations of the doping concentration rate of C545T have a effect on the voltage-current density characteristics. The voltage-current characteristics are quite consistent with the results which were experimentally determined in a previous reference paper. In addition, the voltage-luminance characteristics were greatly improved, and the luminous efficiency was improved three times. In order to analyze these driving mechanism, we have investigated the distribution of electric field, charge density of the carriers, and recombination rates in the inner of the OLED devices.

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.

Passivation Layers for Organic Thin-film-transistors

Inorganic layers, such as SiOxNy and SiOx deposited using plasma sublimation method, were tested as passivation layer for organic thin-film-transistors (OTFTs). OTFTs with bottom-gate and bottom-contact structure were fabricated using pentacene as organic semiconductor and an organic gate insulator. SiOxNy layer gave little change in characteristics of OTFTs, but SiOx layer degraded the performance of OTFTs severely. Inferior barrier properties related to its lower film density, higher water vapor transmission rate (WVTR) and damage due to process environment of oxygen of SiOx film could explain these results. Polyurea and polyvinyl acetates (PVA) were tested as organic passivation layers also. PVA showed good properties as a buffer layer to reduce the damage come from the vacuum deposition process of upper passivation layers. From these results, a multilayer structure with upper SiOxNy film and lower PVA film is expected to be a superior passivation layer for OTFTs.

Efficient Organic Light-emitting Diodes with Aluminum-doped Zinc Oxide Anodes

Properties of organic light-emitting diodes (OLEDs) with aluminum-doped zinc oxide (ZnO:Al) anodes showed different behaviors from OLEDs with indium tin oxide (ITO) anodes according to driving conditions. OLEDs with ITO anodes gave higher current density and luminance in lower voltage region and better EL and power efficiency under lower current density conditions, However, OLEDs with ZnO:Al anodes gave higher current density and luminance in higher voltage region over about 8V and better EL and power efficiency under higher current density over . These seemed to be due to the differences in conduction properties of semiconducting ZnO:Al and metallic ITO. OLEDs with ZnO:Al anodes showed nearly saturated efficiency under high current driving conditions compared with those of OLEDs with ITO anodes. This meant better charge balance in OLEDs with ZnO:Al anodes. These properties of OLEDs with ZnO:Al anodes are useful in making bright display devices with efficiency.