Negative threshold voltage shift for LTPS TFTs under X-ray irradiation and gate bias

Ya Hsiang Tai, Shan Yeh*, Po Chun Chan, Yi Shen Li, Shih Hsuan Huang, Cheng Che Tu, Ting Chang Chang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

In this paper, the behavior of the low-temperature polycrystalline-silicon (LTPS) thin film transistors (TFTs) during X-ray irradiation and gate bias voltage (VG) simultaneously is analyzed. Both n-type and p-type LTPS TFTs show negative shifts of threshold voltage under same dose of X-ray irradiation, regardless of the VG polarity, while the field effect mobility of n-type LTPS TFT keeps fairly well. The degradation of subthreshold swing is attributed to the interface states, which can be repaired by 300 °C annealing. A model is proposed to explain the results for different VG, and verified by changing the thickness of the gate oxide. More irradiation-induced holes are trapped by the far defects owing to the electric field. This study can be helpful to develop more stable devices or circuits for the application of X-ray image sensors.

Original languageEnglish
Article number095012
JournalSemiconductor Science and Technology
Volume34
Issue number9
DOIs
StatePublished - 13 Aug 2019

Keywords

  • Gate bias
  • Gate insulator
  • Low-temperature polycrystalline silicon (LTPS)
  • Thin-film transistor (TFT)
  • X-ray

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