AN EXPERIMENTAL-STUDY ON THE SHORT-CHANNEL EFFECTS IN UNDERGATED POLYSILICON THIN-FILM TRANSISTORS WITH AND WITHOUT LIGHTLY DOPED DRAIN STRUCTURES

Short-channel effects are studied for undergated polysilicon thin-film transistors (TFT's). Although a simple lightly doped drain (LDD) structure can minimize the effects, a much longer LDD region is required than in a bulk transistor. In addition to significant effects similar to bulk transistors, the leakage current is more affected by variations of the channel length and drain bias than it is in a bulk transistor due to the granular structures of the polysilicon films and the enhanced junction field in the fully depleted structure. As a result, variations of the ON current, OFF current, and their ratio are dramatic without the LDD structure.