Impact of the Source/Drain Electrode Process on the Mobility-Threshold Trade-Off for InSnZnO Thin-Film Transistors

In this work, the source/drain (S/D) electrode process is considered to have a great impact on the mobility (μ FE )–threshold ( V th ) trade-off for high-mobility amorphous oxide semiconductor (AOS) thin-film transistors. High-mobility AOS materials have worse oxygen-fixation ability compared to InGaZnO. In this work, we show that this is the case for the Mo S/D electrode process on InSnZnO channels and has a great impact on the mobility-threshold trade-off. Oxygen vacancy gradients are observed in the depth profile X-ray photoelectron spectroscopy analysis on InSnZnO after Mo S/D deposition and show a bigger change in oxygen vacancies ( V O ) between the surface and inner layers and thicker compared to InGaZnO. This leads to an obvious negative shift in V th or even no switching characteristic. Postprocessing such as oxygen-plasma treatment can make V th positive but degrade the μ FE . In situ replenishing oxygen via adopting ITO S/D electrodes deposited in an oxygen-containing atmosphere facilitates the achievement of excellent overall electrical characteristics, with μ FE up to 87.1 cm 2 /Vs, V th ∼ −0.64 V, and I on / I off ∼ 2.3 × 10 8 .