AVALANCHE-INDUCED EFFECTS IN POLYSILICON THIN-FILM TRANSISTORS

We present a comparison of experimental data and two-dimensional numerical simulations of polysilicon thin-film transistors (TFT's) which shows that avalanche multiplication causes both the "kink" effect in their output characteristics and the reduction of threshold voltage in short-channel devices. We show that exactly the same physical model for avalanche multiplication gives very good agreement between simulations and experimental data for both these effects. Finally we demonstrate that it is the presence of grain boundaries or traps in the polysilicon that causes avalanche effects to be much greater than in comparable single-crystal silicon devices.