Remarkable Improvement in Foldability of Poly-Si Thin-Film Transistor on Polyimide Substrate Using Blue Laser Crystallization of Amorphous Si and Comparison with Conventional Poly-Si Thin-Film Transistor Used for Foldable Displays

Highly robust poly-Si thin-film transistor (TFT) on polyimide (PI) substrate using blue laser annealing (BLA) of amorphous silicon (a-Si) for lateral crystallization is demonstrated. Its foldability is compared with the conventional excimer laser annealing (ELA) poly-Si TFT on PI used for foldable displays exhibiting field-effect mobility of 85 cm(2) (V s)(-1). The BLA poly-Si TFT on PI exhibits the field-effect mobility, threshold voltage (V-TH), and subthreshold swing of 153 cm(2) (V s)(-1), -2.7 V, and 0.2 V dec(-1), respectively. Most important finding is the excellent foldability of BLA TFT compared with the ELA poly-Si TFTs on PI substrates. The V-TH shift of BLA poly-Si TFT is approximate to 0.1 V, which is much smaller than that (approximate to 2 V) of ELA TFT on PI upon 30 000 cycle folding. The defects are generated at the grain boundary region of ELA poly-Si during folding. However, BLA poly-Si has no protrusion in the poly-Si channel and thus no defect generation during folding. This leads to excellent foldability of BLA poly-Si on PI substrate.