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

We found that for unpassivated short-channel TFTs, hot carrier stress-induced 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-trapped charges are responsible for the degradation. For others with narrow channel 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-induced grain boundary traps near the drain side. Additionally, the stress-induced degradations of passivated TFTs with various geometries are identical. The increased defect density dominates the mechanism since the hot-carrier stress tends to break the passivated SI-H bonds. (C) 2000 Elsevier Science Ltd. All rights reserved.