A SIMPLER 100-V POLYSILICON TFT WITH IMPROVED TURN-ON CHARACTERISTICS

An improved polysilicon high-voltage thin-film transistor (HVTFT) structure is proposed for eliminating the current-pinching phenomenon often observed in the conventional offset-gate polysilicon HVTFT's. The new HVTFT employs, in lieu of ion implantation, a metal field plate overlapping the entire offset region to control the conductivity of the offset region. By properly biasing the field plate to distribute the drain electric field at both ends, high-voltage operation of up to 100 V, suitable for many large-area applications, is achieved. Good turn-on characteristics without current-pinching effects are consistently obtained. Moreover, the new structure also eliminates the lightly doped drain implant required in conventional offset-gate HVTFT's, resulting in a simpler and more reproducible process. © 1990 IEEE