Correlation of trap states with negative bias thermal illumination stress stabilities in amorphous In–Ga–Zn–O thin-film transistors studied by photoinduced transient spectroscopy

Abstract

Negative bias thermal illumination stress (NBTIS) stabilities in amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) were studied by photoinduced transient spectroscopy (PITS). The degradation of TFT performance correlated with trap states in the channel region of a-IGZO TFTs with an etch stop layer (ESL). A prominent peak at approximately 100 K was observed in a-IGZO formed under a partial pressure (p/p) of 4% O2. With increasing O2 p/p, an apparent shoulder of around 230 K appeared in PITS spectra. A higher flow rate of SiH4/N2O for the ESL deposition induced trap states associated with the 230 K peak. The peak at approximately 100 K could originate from the depletion of Zn by preannealing, while the peak at approximately 230 K should be attributed to the oxygen-deficient and/or Zn-rich defects due to the formation of OH in a-IGZO. The trap states in a-IGZO TFTs gave rise to degradation in terms of NBTIS. The threshold voltage shift (ΔVth) was 2.5 V, but it increased with the O2 p/p as well as the flow rate of SiH4/N2O for ESL deposition. The time dependence of ΔVth suggested that hydrogen from the ESL and/or in the a-IGZO thin films was incorporated and modified the trap states in the channel region of the a-IGZO TFTs.