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

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 irradiati...

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Bibliographic Details
Published in:Semiconductor science and technology 2019-09, Vol.34 (9), p.95012
Main Authors: Tai, Ya-Hsiang, Yeh, Shan, Chan, Po-Chun, Li, Yi-Shen, Huang, Shih-Hsuan, Tu, Cheng-Che, Chang, Ting-Chang
Format: Article
Language:English
Subjects:
gate bias
gate insulator
low-temperature polycrystalline silicon (LTPS)
thin-film transistor (TFT)
X-ray
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Summary: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.
ISSN:0268-1242
1361-6641
DOI:10.1088/1361-6641/ab3157