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.