Low Temperature Poly-Si TFT Technology
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Low Temperature Poly-Si TFT Technology T. Noguchi1,2, D.Y. Kim1, J.Y. Kwon1, K.B. Park1, J.S. Jung1, W.X. Xianyu1, H.X. Yin and H.S. Cho1, 1 Sumsung Advanced Institute of Technology (SAIT), P.O. Box 111, Suwon 440-600, Kyungi, Korea, 2Sungkyunkwan University, Kyungi, Korea ABSTRACT Low temperature poly-Si TFT technology is reviewed and is discussed from a view point of device, fabrication process, and its possibility as FPD (Flat Panel Display) application. After the appearance of crystallization technique of SPC (Solid Phase Crystallization) using FA (Furnace Annealing) or ELA (Excimer Laser Annealing) using UV (Ultra-Violet) beam, the electronic property of poly-Si thin-film, which relates to the crystalinity of the grains, was improved drastically, and the process temperature for the TFT fabrication had been reduced below 600℃ down to 400℃. As a result, improvement of device characteristic of poly-Si TFT such as an enhancement of carrier mobility or a reduction of leakage current has been studied intensively for the application to FPD (Flat Panel Display) on glass. Currently, extensive study is being done in order to realize a more functional SOG (System on Glass). By reducing the TFT process temperature down to 200℃ or below and by modifying a design for the device structure or the circuit in the pixel, O-LED (Organic LED) FPD addressed by uniform poly-Si TFTs is expected to mount on flexible plastic substrate such as on PES (PolyEtherSulphone). The poly-Si TFT has a possibility to develop as a smart system on plastic panel for unique applications as well as the conventional Si LSI in the ubiquitous IT (Information Technology) era. 1. INTRODUCTION Si TFT has been developed remarkably in the last 20 years and plays an important role for FPD application. The Poly-Si TFT had been developed for high-resolution LCD panel with peripheral circuit on quartz glass using high temperature process.1) Subsequently, the LTPS (Low Temperature Poly-Si) TFT on low-cost glass was also applied to LCD panel with peripheral circuit, and has a further possibility for highly functional system i.e. SOG.2) For the AM FPD panel, O-LED Display of direct emission as well as LCD of indirect emission has been actively reported. The poly-Si TFT performance can be improved by optimizing the device structure and the effective crystallization process such as SPC,3, 4) ELC (Excimer Laser Crystallization) or MIC (Metal Induced Crystallization). Poly-Si TFT can be realized not only on glass but also on flexible metal or plastic. In order to realize more flexible and functional FPD, many efforts are being done on further reduction of the process temperature and the improvement of the device characteristic. On the other hand, following a trend of lowering the voltage and shrinkage of device size by a requirement of display with high resolution, a uniformity issue including reliability for the TFT becomes important. In particular, pixel in AM FPD requires uniform and stable characteristics of TFT for the driving. An optimum TFT structure such
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