Role of environmental and annealing conditions on the passivation-free in-Ga-Zn-O TFT

Chur Shyang Fuh, Simon Min Sze, Po-Tsun Liu*, Li Feng Teng, Yi Teh Chou

*Corresponding author for this work

Research output: Contribution to journalArticle

60 Scopus citations

Abstract

We examined the characteristics of passivation-free amorphous In-Ga-Zn-O thin film transistor (a-IGZO TFT) devices under different thermal annealing atmospheres. With annealing at higher temperature, the device performed better at the above-threshold operation region, which indicated the film quality was improved with the decrease of defects in the a-IGZO active region. The mobility, threshold voltage and subthreshold swing of a-IGZO TFT annealed at 450 °C was 7.53 cm2/V s, 0.71 V and 0.18 V/decade, respectively. It was also observed that the a-IGZO was conductive after thermal annealing in the vacuum, due to the ease of oxygen out-diffusion from the a-IGZO back channel. The oxygen deficiency resultantly appeared, and provided leaky paths causing electrical unreliability when TFT was turned off. In contrast, the annealing atmosphere full of O2 or N2 would suppress the oxygen diffusion out of the a-IGZO back channel. The worst Vth degradation of a-IGZO TFT after positive gate bias stress and negative gate bias stress (NGBS) was about 2 V and - 2 V, respectively. However, the Vth shift in the NGBS testing could be suppressed to - 0.5 V in vacuum chamber. Material analysis methods including X-ray photoelectron spectroscopy and scanning electron microscopy were used to investigate the change of a-IGZO film after different thermal annealing treatments. The variation of O 1s spectra with different annealing atmospheres showed the consistence with our proposed models.

Original languageEnglish
Pages (from-to)1489-1494
Number of pages6
JournalThin Solid Films
Volume520
Issue number5
DOIs
StatePublished - 30 Dec 2011

Keywords

  • Annealing environment
  • InGaZnO TFT
  • Operation model
  • Reliability mechanism
  • Thermal annealing

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