Characteristics of High Mobility Polysilicon Thin-Film Transistors Using Very Thin Sputter-Deposited Si02 Films

Polysilicon thin-film transistors with various gate oxide thicknesses ranging from 94 to 7 nm using sputter-deposited Si02 films were fabricated and their electrical characteristics were studied to explore the possibilities of enhancing the TFT characteristics by scaling down the gate oxide thickness. It was found that the threshold voltage and the subthreshold slope decrease linearly as the gate oxide thickness is reduced while the filed effect mobilities stay constant. The breakdown electric field of the gate oxide increases as the gate oxide thickness decreases and is over 10 MV/cm when the thickness is less than 20 nm. The polysilicon TFT with the 7-nm gate oxide, the thinnest in this work, showed excellent characteristics: threshold voltage of 0.44 V, subthreshold slope of 110 mV/dec, field effect mobility of 97 cm2/Vs.