Amorphous silicon thin film transistors

Abstract

Abstract The effect of various gate insulators on the electrical properties of the amorphous silicon thin film transistors (TFTs) has been investigated. When the silicon nitride is used as the gate insulator, the on/off current ratio of the TFT is found to exceed 106 and the subthreshold swing is 0.4 V/decade. The highest field‐effect mobility achieved is about 0.42 cm2/V‐sec. A channel thickness of 50 nm is found to be appropriate to achieve good performance and the source/gate contact overlap of 0.5 μm eliminates the source resistance problem. When the electron gun evaporated silicon dioxide (SiO1.68) is used as the insulator, the highest field‐effect mobility of TFT in the saturation region of the I DS versus V DS curve is 5.1 cm2/‐sec. Actually, the electron drift velocity has saturated at 1.7 × 104 cm/sec, this is the first report of the electron saturation velocity in amorphous silicon alloy. The on/off current ratio exceeds 105 and the subthreshold swing is ranged from 0.25 to 0.5 V/decade.