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 (ΔV th) 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 ΔV th 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.

Electrical Characterization of Zinc‐Rich Amorphous In‐Ga‐Zn‐O Thin Film Transistors

“…The variation of transfer curves by NBTIS test obtained from the a‐IGZO TFTs corresponding to Figure is shown in Figure . As shown in Figure , when the Zn content was relatively small, the transfer curves changed to have a tail at the rise of the drain current by the NBTIS test, similar to the previous report . While the Zn metal ratio increased, the transfer curves turned into a change having a hump shape, and furthermore, they changed in parallel.…”

“…The PITS is a variation of DLTS effective to evaluate the trap states in the back channel region of the a‐IGZO TFTs by using test devices equivalent to the actual TFT structures . The principle and measurement procedure of PITS has been described elsewhere . Briefly, the transient photo‐currents, excited by light irradiation of a UV laser with a wavelength of 375 nm (the pulse width was 100 ms), were measured and analyzed in the temperature range between 70 and 350 K. Based on the theory of Fourier transformation DLTS, the b1 coefficient obtained from a first term of Fourier transformation was used for evaluation.…”

Improvement of Stress Stability in Back Channel Etch-Type Amorphous In-Ga-Zn-O Thin Film Transistors with Post Process Annealing

“…17,18 The b1 coefficient obtained from a first term of Fourier transformation was used for evaluation. 15,16 Glass sub.…”

“…6b, a prominent peak with a maximum b 1 of around 100 K was observed, which is consistent with that in the previous report. 16 Here, since the S/D over-etching was performed adequately for suppressing the degradation of the value of SS, it is considered that the influence of the continuous gap states can be neglected in the BCE structure. Therefore, the results suggest that the broadening of the PITS spectra from PITS -ESL1 to PITS -BCE1 was induced by the applied S/D process, consisting of S/D deposition and S/D etching.…”

“…Recently, using PITS, Hayashi et al made a comparative study on the correlation of electron traps in the channel region of a-IGZO TFTs with negative bias, thermal and illumination stress (NBTIS) stabilities. 16 As for the BCE-TFTs, the effects of the BCE process on the electronic states should be clarified. Furthermore, the recovery is the issue to be examined.…”