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 (TFTs). 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 results, variations of the ON current, OFF current, and their ratio are dramatic without the LDD structure.<>