In Situ Rad-Hard Amorphous Zinc–Indium–Tin Oxide Thin-Film Transistors

Radiation-hardness is crucial for the realization of high-performance radar, large-area sensor arrays, and radiation dose monitoring for aerospace and nuclear applications. In this study, ex situ and in situ radiation hardness of solution-processed metal-oxide thin-film transistors (TFTs) are investigated under ionizing radiation exposure such as proton and gamma-ray. Detailed X-ray photoelectron spectroscopy analysis revealed that a significant number of oxygen vacancies and subsequent hydroxide are generated in the irradiated channel and result in negative threshold voltage shifts, while increasing the subthreshold swing and mobility values for its TFT devices. By employing different metal compositions for the channel layer, it has been demonstrated that large oxygen vacancy generation energy of SnO2 and ZnO could suppress vacancy generation and lead to radiation-hardness. Moreover, optimization in the composition lead to the identification of amorphous zinc–indium–tin oxide (Zn–In–Sn–O or ZITO) where the synergetic combination of structural plasticity of Zn, defect tolerance of Sn, and high electron mobility of In exhibits a synergetic effect for radiation-hardness. With a blending ratio of 4:1:1 for Zn/In/Sn, ZITO TFTs show superior ex situ radiation-hardness compared to the other oxides such as In–Ga–Zn–O, Zn–O, Ga–Sn–O, Ga–In–Sn–O, and Ga–Sn–Zn–O. For in situ irradiation, a negative threshold voltage shift was observed accompanied by increased mobility and increased off- and leakage currents, thereby proposing three factors for the degradation mechanism: (i) increase of channel conductivity, (ii) interface-trapped and dielectric-trapped charge buildup, and (iii) trap-assisted tunneling in the dielectric. Finally, we demonstrate in situ radiation-hard oxide-based TFTs by employing a ZITO channel, a thin dielectric (50 nm SiO2), and a passivation layer for ambient exposure. This device exhibits excellent stability with an electron mobility of ∼10 cm2/V s with Δ<i>V</i>th of &lt;3 V under real-time (15 kGy/h) gamma-ray irradiation in an ambient atmosphere.