The development and characterization of MG poly-Si NW-TFTs and the preliminary investigation of NW TFT-SONOS with independent DG have been studied in this thesis. For the purpose of further improving device performance, some valuable researches for the future work are suggested as follows:
1. In general, the fine-grain structure of poly-Si TFT is considered to affect the carrier transport and device performance. We have already discussed the MG poly-Si NWTFT prepared by solid-phase crystallization (SPC) in this thesis, but still various methods are known to increase the grain size of the poly-Si thin film, including excimer laser annealing (ELA) and metal-induced lateral crystallization (MILC). Recently, MILC method has been successfully adopted in single side-gated NWTFT [4-1], it will be interesting to apply the method to the MG NWTFT to further improve the device performance.
2. Since the poor endurance characteristics of NW-SONOS devices are attributed to the irregular NW profile and poor quality of TEOS oxide, how to eliminate the tips of the NW channels and fabricate high quality tunneling oxide are important issues that need to be addressed.
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(a)
(b)
Fig. 2-1 Top view and cross-sectional view of inverse-T gate NWTFT (a) and inverse-T double-gate NWTFT (b).
Si Substrate Thermal Oxide
Si Substrate Si Substrate Thermal Oxide Thermal Oxide
Fig. 2-2 (a) Deposition of in-situ-doped n+ poly-Si.
Si Substrate Thermal Oxide
Si Substrate Si Substrate Thermal Oxide Thermal Oxide
Fig. 2-2 (b) Definition and formation of inverse-T gate.
Si Substrate Thermal Oxide
Si Substrate Si Substrate Thermal Oxide Thermal Oxide
Fig. 2-2 (c) Deposition of inverse-T gate oxide and poly-Si active layer.
Si Substrate Thermal Oxide
Si Substrate Si Substrate Thermal Oxide Thermal Oxide
Fig. 2-2 (d) Source/Drain ion implantation.
Si Substrate
Fig. 2-2 (e) Definition of source/drain and formation of NW channel (ITG structure).
Si Substrate
Fig. 2-2 (f) Deposition of top gate oxide and formation of top gate (ITDG structure).
50nm
80nm 40nm
50nm
80nm 40nm
Fig. 2-3 Cross-sectional TEM image of NW channels with inverse-T gate.