The Influence of Passivation Layer Thickness on Radiation Hardness of ZnO Thin Film Transistors Subjected to Proton Irradiation.*

We have investigated the effect of passivation layer thickness on the radiation hardness of ZnO thin film transistors (TFTs). ZnO TFTs with three different passivation layer thicknesses were prepared to obtain the maximum proton distribution in either the ZnO channel layer, ZnO/SiO₂ interface, or SiO₂ dielectric layer. The samples were irradiated using a 200 keV proton beam with the fluence of 1×10¹⁴ protons/cm². The depth distribution of the non-ionizing energy loss (NIEL) calculated by TRIM simulation data has shown a significant variation along the depth of these three samples. The sample with maximum proton distribution within the ZnO layer showed negligible degradation in device performance compared to unirradiated devices. However, devices with the maximum of proton distribution at either the ZnO/SiO₂ interface or in the SiO₂ dielectric layer exhibited larger degradation in device characteristics after proton irradiation. Therefore, we observe that caution should be exercised when studying the radiation hardness of proton-irradiated ZnO TFTs since variation in thickness of the passivation layer can result in significantly different device performance after the irradiation.