Dimensional effects on the reliability of polycrystalline silicon thin-film transistors

We found that for unpassivated short-channel TFTs, hot carrier stress-induc ed degradation phenomena are different with various channel geometries. For device with a wide channel width, the threshold voltage is increased while the subthreshold swing is almost unchanged. The stress-induced oxide-trapp ed charges are responsible for the degradation. For others with narrow chan nel widths after stress, on the contrary, the subthreshold swing and I-min are increased, the trap density is greatly increased and the trap-enhanced kink effect is also observed. This is due to the generation of stress-induc ed grain boundary traps near the drain side. Additionally, the stress-induc ed degradations of passivated TFTs with various geometries are identical. T he increased defect density dominates the mechanism since the hot-carrier s tress tends to break the passivated SI-H bonds. (C) 2000 Elsevier Science L td. All rights reserved.