Effects of channel composition and gate dielectrics on the stability of a-IGZO TFTs

摘要

The electrical and optical stability of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) related to the channel composition (the concentration of oxygen vacancy, Vo2+) and gate dielectrics are discussed. With the filling of Vo2+, the electron density (Ne) in a-IGZO decreases from 7.5 to 3.8 (×1016cm‐3) with the increase of Fermi level and decrease of density of deep charged traps, and therefore the electrical stability of TFTs decreases from A Vth of 4.5 to 10V. The optical stability of a-IGZO TFTs is also sensitive to the Vo2 +. With the increase of Vo2+ the absorption increases and Eg decreases for a-IGZO, therefore the number of generating photo-electrons increases and the stability of TFT decreases. The SiNx-gated TFT shows good electrical stability, but its optical stability is an issue, which shows a larger off-state photo leakage current (△ Id~13μA) and decrease of Vth (|A Vth|> 14V) than those of the SiO2-gated TFT (△ Id~12 nA, |△ Vth|~8V). The model of charge trapping at the interface of gate dielectric/a-IGZO is only valid for the mechanism of electrical stability. It is proposed that due to the larger absorption of visible light of SiNx gate dielectric, and the smaller △EV between SiNx and a-IGZO film, the photo created holes carriers in a-IGZO channel can be injected more easily into SiNx during light on resulting a significant increase of Ne in a-IGZO, therefore an apparent decrease of Vth for TFT.