Effect of X-ray irradiation on a-IGZO and LTPS thin-film transistors for radiography applications

Abstract

Abstract The effects of X-ray irradiation on amorphous indium-gallium-zinc oxide (a-IGZO) and low-temperature polysilicon (LTPS) thin-film transistors (TFTs) were investigated. A comparison of the electrical characteristics of the TFTs at different stages of exposure to X-rays was conducted. After X-ray irradiation, the a-IGZO TFTs maintained their performance, while the LTPS TFTs showed considerable performance degradation. A distinct negative threshold voltage shift occurred in the LTPS TFTs under X-ray irradiation. In addition, the electrical parameters including mobility, subthreshold swing and off-current were significantly deteriorated. In addition, the binding energy shift of Si 2p peaks in the phase transition region of the interlayer between Si and SiO2 was confirmed by XPS depth profile analysis. This result indicates that permanent damage to the LTPS crystalline structure was induced under X-ray exposure. Under the same doses of X-ray irradiation, the a-IGZO film did not exhibit any notable change, indicating the tolerance of a-IGZO to X-ray irradiation. Therefore, we expect a-IGZO to be applied in the active matrix backplane of medical X-ray detectors for use for prolonged periods of time. This work not only provides systemic studies on the effects of X-rays on semiconductor materials but also proposes an alternative material to highly endurable X-ray detectors.