High-Mobility,High-Photostability Tetravalent-Terbium-DopedIndium–Tin–Zinc-Oxide Thin-Film Transistors with a Stacked-ChannelStructure

The trade-off between mobility and stability is the main problem for amorphous oxide semiconductor (AOS) thin-film transistors (TFTs). In this work, a high-mobility and good-photostability Tb-doped indium–tin–zinc oxide (Tb:ITZO) AOS is studied. The ITZO TFT without Tb doping had a mobility of as high as 49.4 cm²·V^–1·s^–1 but exhibited poor stability under negative bias illumination stress (NBIS). After Tb doping, the NBIS stability of the TFTs improved greatly, but the mobility reduced to 37.9 cm²·V^–1·s^–1. The great improvement of the NBIS stability of the Tb:ITZO TFTs is attributed to the charge-transfer transition between Tb4<i>f</i>⁷O2<i>p</i>⁶ and Tb4<i>f</i>⁸O2<i>p</i>⁵ that would reduce the lifetime of the photoinduced electrons and the ionized oxygen vacancies. Increasing O₂ flow rates during sputtering would further enhance the NBIS stability but decrease the mobility seriously. To further improve the mobility of the Tb:ITZO TFTs, a stacked-channel TFT was fabricated by using the same Tb:ITZO target (sputtering with different O₂ flow rates). The mobility increased to 40.4 cm²·V^–1·s^–1, and it also exhibited good NBIS stability. The mobility increment of the stacked-channel TFTs is ascribed to the conduction path confinement of the front channel by the conduction band barrier at the bilayer interface. This work provides a prominent AOS material and a simple way to break the trade-off between the mobility and stability of the AOS-TFTs.