Excimer laser crystallized poly-Si TFTs on plastic substrates

Abstract

Excimer laser crystallized poly-Si TFTs, integrated both for drive circuits and pixels, on a glass substrate for use in various applications, such as, flat panel display are now available in the market. These poly-Si TFTs on glass are generally prepared by excimer laser crystallization of plasma enhanced chemical vapor deposited amorphous silicon films, which, are generally deposited in the substrate temperature range of 300 degree(s)C-400 degree(s)C. Changing the TFT backplate from glass to plastic will reduce the wight, but transparent plastic substrates are generally only temperature-resistant up to 125 degree(s)C. We have focused therefore, on reducing the maximum processing temperature to 110 degree(s)C. Our approach utilizes sputtered a- Si films for crystallization, because they contain no hydrogen and can be crystallized by an excimer laser even if deposited at room temperature. We report high-quality poly-Si obtained by pulse laser crystallization on a plastic substrate coated with a buffer layer. Transmission electron microscope was used to confirm the crystallinity of the films. A doping technique for source and drain compatible with a low temperature wide area substrate, based on excimer laser annealing, has been developed. Self-aligned top-gate TFTs fabricated on a plastic substrate at a substrate temperature of 100 degree(s)C are reported. Transistor field effect mobility of 250 cm<SUP>2</SUP>/V.s and s sub-threshold swing of 0.16 V/decade were measured in these devices.