ANALYSIS OF CURRENT VOLTAGE CHARACTERISTICS OF LOW-TEMPERATURE-PROCESSED POLYSILICON THIN-FILM TRANSISTORS

The relationship between device performance and trap state density in polysilicon films was investigated. The density in the silicon energy gap was obtained by fitting the calculated on-state current versus gate voltage curve to the measured one for low-temperature (less-than-or-equal-to 600-degrees-C) processed polysilicon TFT's fabricated under various conditions, such as different deposition temperatures and annealing methods for crystallization. On-state current was markedly improved by reducing the density near band edges in the gap, and the improvement was realized by depositing the films at around 550-degrees-C in an LPCVD system or employing laser annealing instead of thermal annealing at 600-degrees-C. Off-state current was reduced to a great extent by reduction of the density around the midgap by using a plasma-hydrogenation technique.