Joon-Chul Goh

70.4: A 14.1inch AMOLED Display using Highly Stable PECVD based Microcrystalline Silicon TFT Backplane

We have developed a 14.1 inch AMOLED display using microcrystalline silicon (mc-Si) TFTs. Microcrystalline silicon was deposited using conventional 13.56MHz Plasma Enhanced Chemical Vapor Deposition (PECVD). Detailed thin film characterization of mc-Si films was followed by development of mc-Si TFTs which show a field effect mobility of around 0.7∼1.0cm2/V.s. The mc-Si TFTs show no significant shift in threshold voltage when applied with a long time constant current stress, indicating a stable TFT backplane. The mc-Si TFTs were successfully integrated in a 14.1 inch AMOLED display. The display shows no significant current decrease in the driving TFT of the 2T circuit, even after long time of lifetime tests. Along with improved lifetime for AMOLED display, the development of mc-Si TFTs using conventional 13.56 MHz PECVD system offers significant cost advantages over other laser or non-laser polysilicon TFT technologies for AMOLED.

49.1: A 14.1 inch Full Color AMOLED Display with Top Emission Structure and a‐Si TFT Backplane

A structure and a design of device were developed to fabricate large-scale active matrix organic light-emitting diode (AMOLED) display with good color purity and high aperture ratio. With these technologies, we developed a full color 14.1 inch WXGA AMOLED display. For the integration of OLED on an active matrix a-Si TFT backplane, an efficient top emission OLED is essential since the TFT circuitry covers a large position of the pixel aperture. These technologies will enable up the OLED applications to larger size displays such as desktop monitors and TVs.

New Fraction Time Annealing Method For Improving Organic Light Emitting Diode Current Stability of Hydorgenated Amorphous Silicon Thin-Film Transistor Based Active Matrix Organic Light Emitting Didode Backplane

We propose and fabricate a new hydrogenated amorphous silicon (a-Si:H) thin-film transistor (TFT) pixel employing a fraction time annealing (FTA), which can supply a negative gate bias during a fraction time of each frame rather than the entire whole frame, in order to improve the organic light emitting diode (OLED) current stability for an active matrix (AM) OLED. When an electrical bias for an initial reference current of 2 µA at 60 °C is applied to an FTA-driven pixel more than 100 h and the temperature is increased up to 60 °C rather than room temperature, the OLED current is reduced by 22% in the FTA-driven pixel, whereas it is reduced by 53% in a conventional pixel. The current stability of the proposed pixel is improved, because the applied negative bias can suppress the threshold voltage degradation of the a-Si:H TFT itself, which may be attributed to hole trapping into SiNx. The proposed fraction time annealing method can successfully suppress Vth shift of the a-Si:H TFT itself due to hole trapping into SiNx induced by negative gate bias annealing.

P-137: An Accurate Electrical Model of a Liquid Crystal Cell in Active-Matrix LCD

We propose an electrical model of a pixel in a matrix-driven LCD panel to accurately anticipate transient optical responses. We present a method to get accurate transmittance/capacitance vs. voltage data. Our model can be applied to find overdrive values to improve response characteristics.

P-259L: Late-News Poster: A 14inch Uniform AMOLED Display with Low Cost PECVD Based Microcrystalline Silicon TFT Backplanes

This paper discusses development of uniform 14.1 inch AMOLED display using PECVD based microcrystalline silicon (mc-Si) TFTs. Microcrystalline silicon was deposited using conventional 13.56 MHz Plasma Enhanced Chemical Vapor Deposition (PECVD) with novel gas precursors. The mc-Si TFTs show a field effect mobility of around 1cm2/V.s and off-current less than 1pA. Electrical stress on mc-Si TFTs for a long time shows no significant threshold voltage shift indicating a stable TFT backplane. Significant uniformity improvements were made with novel TFT structure to give uniform AMOLED display. The deposition time for mc-Si TFTs was significantly reduced by using a thin mc-Si layer. Mc-Si TFT backplanes using conventional PECVD equipment offers significant cost advantages over other competing laser and non-laser polysilicon TFT technologies for AMOLEDs.

P-177: A 14.1-in. Full-Color Polymer-LED Display with a-Si TFT Backplane by Ink-Jet Printing

We have developed a 14.1 inch full color polymer LED display, based on an a-Si TFT backplane, using ink jet printing, which does not show visible swathe marks during display operation. To remove the swathe marks, we have developed the single path printing technology for the hole-conduction layer deposition to significantly reduce the complexity of interlacing printing across the panel, which is known as an alternative to remove the swathe marks. In addition, we have adopted the interlayer process to increase the lifetime of ink jet printed displays. These technologies will enable the scale-up of the ink jet printed AMOLED applications to larger size displays, such as desktop monitors and TVs.

13.2: Highly Stable a-Si:H TFT Pixel for Large Area AMOLED by Employing Both Vth Storing and the Negative Bias Annealing

Highly stable voltage programmed a-Si:H TFT pixel circuit for AMOLED, which employs both Vth-compensation and negative bias annealing, is proposed and fabricated. Experimental results, after 60 hours electrical stress at elevated temperature (60°C) show that the OLED current stability in the proposed pixel is considerably improved compared with a conventional 2-TFT pixel, Vth-compensated pixel, and negative bias annealed pixel, respectively. The proposed pixel can reduce the degradation of a-Si:H TFT by employing negative bias annealing store Vth of a-Si:H TFT so that highly stable and uniform a-Si:H TFT backplane for AMOLED. Our proposed pixel may be suitable for highly stable AMOLED employing the a-Si:H TFT.