The effects of deposition conditions and annealing temperature on the performance of gallium tin zinc oxide thin film transistors

Abstract

In this work the performance of bottom gate thin film transistors (TFTs) with transparent amorphous gallium tin zinc oxide (GSZO) active layers fabricated by radio frequency sputter deposition using a single GSZO target on SiO₂/Si wafers will be presented. Trap density and its energetic distribution, and oxygen chemisorption were found to play a critical role in determining the operational characteristics of the device, all of which can be controlled by the oxygen incorporation and substrate temperature during deposition, along with the post-deposition annealing. In addition device instability, with respect to the electrical stress and optical illumination, can be suppressed by suitably tailoring these parameters. TFTs exhibiting a drain current (I_D) of 10^-6 A and on/off current ratio (I_on/off ) of 10⁶ was achieved. A stable TFT has been achieved under electrical stress for 2% oxygen flow exhibiting ΔV_T as low as ~0.5 V for 3hr stress under a gate bias of 1.2 and 12 V, with good optical stability.