Effects of different contents yttrium doping on the electrical performance and stability of bilayer IZO/IYZO thin-film transistors

In this study, the effects of doping with different contents of the rare-earth element yttrium (Y) on the electrical performance of indium zinc oxide (IZO) and bilayer IZO/IYZO thin-film transistors (TFTs) were investigated. Through a rational design, the bilayer IZO/IYZO TFT exhibits the best performance with a Vth of 0.2 V and μFE of 32.6 cm2/V s. X-ray photoelectron spectroscopy band structure analysis demonstrated that, in the IZO/IYZO TFT, a 6-nm highly conductive ultrathin IZO provided free electrons and electron transfer from the IZO layer to the IYZO layer with the formation of band bending, thus increased the carrier mobility of devices. In addition, the 20-nm-thick IYZO layer controlled Ne and Vth by forming a potential barrier (0.38 eV), thereby increasing stability. Moreover, the experimental characterization revealed that Y doping can reduce the carrier concentration, oxygen vacancies, surface defects, and other trap densities of devices. Therefore, the IZO/IYZO TFT demonstrated the best stability with small Vth shifts of −0.9, 0.8, −1.1, and 1.0 V under negative gate bias stress, positive gate bias stress, negative gate bias light illumination stress, and positive gate bias light illumination stress measurements. Overall, the designed IZO/IYZO TFTs open effective pathways for achieving high-performance oxide TFTs.