Cheol-Ho Yu

16.2: World-Best Performance LTPS TFTs with Robust Bending Properties on AMOLED Displays

This study reported a low temperature polycrystalline silicon LTPS thin film transistor TFT fabrication process on plastic substrates for flexible display applications. Polycrystalline silicon poly-Si films were formed by excimer laser annealing ELA method. It was found by ELA thermal simulation that there was around 70 □ on plastic surface during ELA crystallization process. The excimer laser irradiated film was analyzed by using various spectroscopic methods such as X-ray diffraction, scanning electron microscopy, and atomic force microscopy. Dehydrogenation and activation processes were performed by a conventional LTPS method without causing any plastic substrate distortion. The fabricated poly-Si TFT on a flexible backplane shows a very good performance with field effect mobility of 95.3 cm2/Vs, on/off ratio current ratio > 108, and threshold voltage of −1.6 V. Bending tests after a delamination process were also performed with TFT backplane samples.

Effects of high pressure annealing on the characteristics of solid phase crystallization poly-Si thin-film transistors

Integrating circuits into organic light emitting diode displays require fabrication of polycrystalline silicon (poly-Si) based thin-film transistors (TFTs) on glass substrates. In this work we evaluated the use of high pressure annealing (HPA) process of poly-Si films in H2O atmosphere to improve TFT characteristics via reducing defect density in poly-Si films. We attempted to develop a HPA process at temperatures below 600°C without causing any glass distortion and reducing the throughput. The HPA-treated poly-Si film was analyzed using various spectroscopic methods such as Raman, x-ray photoelectron spectroscopy, and transmission electron microscope, and the evaluation of the characteristics of TFTs fabricated by such poly-Si films was made. The heating at 550°C with 1MPa H2O vapor increased the carrier mobility from 8.5to20cm2∕Vs and reduced the absolute value of the threshold voltage from 9.6to6.5V, as compared with the conventional solid phase crystallization (SPC) process. The sub-threshold swings a...