The effect of hydrogen incorporation on the performance of nanocrystalline silicon thin film transistors fabricated by microwave ECR plasma CVD

Nanocrystalline silicon (nc-Si:H) TFT's with the active layers deposited by microwave ECR-CVD were fabricated and characterized using hydrogen dilution as a variable during the Si film deposition. The bottom-gated TFT's were fabricated on SiO₂, glass and polyimide substrates at a temperature of 200-400°C with the introduction of 4-12 mTorr H₂. The correlation between the H₂ dilution and the TFT characteristics was studied and the experimental results were correlated with some theoretical considerations. The TFT on a glass substrate deposited at 400°C with 10 mTorr H₂ showed a field effect mobility of 13.3 cm²/V-s and an ON/OFF current ratio of 4.9×10⁶ with the OFF-state leakage current of 3.7×10^-11 A. We found that, for the same Si film deposition conditions, the TFT's fabricated on polyimide foil have comparable characteristics to the TFT's on glass substrates.