Unusually abrupt switching in submicrometer thin-film transistorsusing a polysilicon film with enhanced grain size

Unusually abrupt drain current change observed in polysilicon thin-film transistors (TFTs) with a channel length and width of 1 μm or smaller is discussed. The polysilicon used to fabricate the devices was deposited by low-pressure chemical vapor deposition (LPCVD) and the grain size of the film was enhanced by silicon ion implantation followed by a low-temperature anneal. The TFTs exhibited an abrupt drain current change of more than five orders of magnitude for a corresponding gate voltage change of less than 40 mV. A self-limiting positive feedback loop due to impact ionization currents and/or a parasitic bipolar effect are suggested as possible explanations