Low-temperature polysilicon TFT with two-layer gate insulator using photo-CVD and APCVD SiO/sub 2/

The performance of polysilicon thin-film transistors (TFTs) formed by a 600 degrees C process was improved using a two-layer gate insulator of photochemical-assisted vapor deposition (photo-CVD) SiO/sub 2/ and atmospheric-pressure chemical vapor deposition (APCVD) SiO/sub 2/. The photo-CVD SiO/sub 2/, 100 AA thick, was deposited on polysilicon and followed by APCVD SiO/sub 2/ of 1000 AA thickness. The TFT had a threshold voltage of 8.3 V and a field-effect mobility of 35 cm/sup 2//V-s, which were higher than those of the conventional TFT with a single-layer gate SiO/sub 2/ of APCVD. Hydrogenation by hydrogen plasma was more effective for the new TFT than for the conventional device.<
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