Origin of Subthreshold Swing Improvement in Amorphous Indium Gallium Zinc Oxide Transistors

The effect of the channel deposition pressure on the device performance of amorphous indium-gallium-zinc oxide (a-IGZO) transistors was investigated. The performance of the fabricated transistors improved monotonously with decreasing chamber pressure at a pressure of 1 mTorr. The field-effect mobility and subthreshold gate swing of the a-IGZO thin-film transistors were dramatically improved to 21.8 cm2/Vs and 0.17 V/decade, respectively, compared to those (11.4 cm2/Vs and 0.87 V/decade) of reference transistors prepared at 5 mTorr. This enhancement in the subthreshold characteristics was attributed to a reduction of the bulk defects of the a-IGZO channel which might result from the greater densification of the a-IGZO films at the lower deposition pressure.