Thin-film transistors on plastic and glass substrates using silicon deposited by microwave plasma ECR-CVD

Thin-film transistors (TFTs) were fabricated on polyimide and glass substrates at low temperatures using microwave ECR-CVD deposited amorphous and nanocrystalline silicon as active layers. The amorphous Si TFT fabricated at 200 °C on the polyimide foil had a saturation region field effect mobility of 4.5 cm²/V-s, a linear region mobility of 5.1 cm²/V-s, a threshold voltage of 3.7 V, a subthreshold swing of 0.69 V/decade, and an ON/OFF current ratio of 7.9 × 10⁶. This large mobility and high ON/OFF current ratio were attributed to the high-quality channel materials with less dangling bond defect states. Nanocrystalline Si TFTs fabricated on glass substrates at 400 °C showed a saturation region mobility of 14.1 cm²/V-s, a linear region mobility of 15.3 cm²/V-s, a threshold voltage of 3.6 V, and an ON/OFF current ratio of 6.7 × 10⁶. TFT performance was mostly independent of substrate type when fabrication conditions were the same.