Threshold Voltage Adjustment in Hybrid-Microstructural ITO-Stabilized ZnO TFTs via Gate Electrode Engineering

When metallic Al was replaced by conductive ITO as the gate electrode (GE) material, the positive threshold voltage (V
_th
) shift of top-gated metal oxide (MO) thin-film transistors (TFTs) was found to be much larger than the work function (WF) difference of the GEs. Using secondary ion mass spectrometry and X-ray photoelectron spectroscopy techniques, it was noted that the permeability of GE materials for hydrogen diffusion out of and oxygen diffusion into the active layers during post-annealing could also affect V
_th
significantly. The hybrid-phase microstructural ITO-stabilized ZnO TFTs with ITO top GEs exhibited relatively good electrical characteristics with a typical V
_th
of 0.5 V and an on-off ratio of over 10
¹⁰
in enhancement operation mode, and robust reliability against gate-bias stress. This letter initiated a new perspective to adjust V
_th
of top-gated MO TFTs via GE engineering.