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

Abstract

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) À1 . 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) À1 , À2.7 V, and 0.2 V dec À1 , 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 %0.1 V, which is much smaller than that (%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.

Extremely foldable LTPS TFT backplane using blue laser annealing for low‐cost manufacturing of rollable and foldable AMOLED display

“…[1][2][3][4][5] However, the use of LTPS by excimer laser annealing (ELA) of a-Si is limited only for mobile displays because of the mother glass size. On the other hand, continuous-wave (CW) laser annealing, in particular, blue laser annealing (BLA), is of increasing interest to replace ELA [6][7][8][9][10][11][12] because ELA cannot support G8 or G10.5/11 for LTPS TFT backplane. Note that the high capital investment of the manufacturing system and operating cost are needed for ELA system and its maintenance.…”

Excellent Mechanical Durability of In‐Folding Stress of Poly‐Si Thin‐Film Transistor on Plastic Substrate Compared with Out‐Folding: Generation of Gate Leakage Currents in Flexible Poly‐Si Thin‐Film Transistor by Out‐Folding and Bias‐Temperature Stress

“…The electrical stability of the LTPS TFT can be affected by the mechanical strain. [ 26–34 ] Contrastingly, electro‐thermal (positive bias temperature stress (PBTS) or negative bias temperature stress (NBTS) after mechanical strain [ 35 ] can also severely deteriorate the electrical characteristics, which needs to be further studied.…”

Large-Scale and Localized Laser Crystallization of Optically Thick Amorphous Silicon Films by Near-IR Femtosecond Pulses

“…However, ultra-low penetration depth of UV light to silicon limits the thickness of -Si film, which can be processed with such an approach. Visible laser radiation (in particular, blue and green lasers operating in CW and pulsed mode [ 1 , 16 , 17 , 18 , 19 , 20 ]) was shown to increase the maximal processing thickness to 150–200 nm; however, this is still not enough to cover all applications. Noteworthy, penetration depth of near-IR radiation into Si, which has good transparency in this spectral range (comparing to UV and visible light), is high enough to drive crystallization inside rather thick -Si films that are required for realistic applications and devices.…”