Improvement of Gate-Insulator/Silicon Interface Characteristics in Amorphous Silicon Thin Film Transistors

Abstract
N-channel Al-top gate type amorphous silicon thin film transistors (a-Si TFTs) were fabricated with an SiO2 gate oxide, never exceeding a substrate temperature of 250° C. A reactive evaporation of SiO powder in an oxygen atmosphere with a flow rate of 2 sccm at a pressure of 1×10-4,Torr was used for forming a good quality interface of SiO2/a-Si. The a-Si TFTs showed characteristics of a low threshold voltage of 0.86 V, a moderate carrier mobility of 1.1 cm2/V· s and a subs-threshold slope of 0.12 V/decade. These characteristics result from a good SiO2/a-Si interface with a density of trapping states of 1.6×1011 cm-2·eV-1.