Thin film transistors on nanocrystalline silicon directly deposited by a microwave plasma CVD

In an effort to develop a low-cost process to fabricate high mobility thin film transistors (TFTs), we present TFTs on nanocrystalline Si formed by a microwave plasma ECR-CVD. Compared with conventional rf plasma, microwave ECR plasma has the advantages of a higher ionization ratio and a lower gas pressure, which lead to higher deposition rate and lower cost for large area electronics. The purpose of this work is to fabricate TFTs on directly deposited nanocrystalline Si films and correlate the TFT performance with the deposition conditions of the nanocrystalline Si. This process produced nanocrystalline Si TFTs on glass with a high field effect mobility of 15.3 cm²/Vs and a small subthreshold swing of 0.45 V/dec for the Si film deposited at 400 °C with 15% H₂ dilution without post-fabrication annealing.