Selective metallization of amorphous-indium-gallium-zinc-oxide thin-film transistor by using helium plasma treatment

In this study, the effects of helium (He) plasma treatment on amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) have been investigated. The He plasma treatment induced a dramatic decrease of the resistivity in a-IGZO thin films from 1.25 ×10⁶ to 5.93 mΩ cm. After 5 min He plasma treatment, the a-IGZO films showed an increase in carrier concentration to 6.70 ×10¹⁹ cm^-3 combined with a high hall mobility of 15.7 cm² V^-1 s^-1. The conductivity improvement was linked to the formation of oxygen vacancies during the He plasma treatment, which was observed by x-ray photoelectron spectroscopy analysis. The a-IGZO films did not appear to be damaged on the surface following the plasma treatment and showed a high transmittance of about 88.3% at a wavelength of 550 nm. The He plasma-treated a-IGZO films were used as source/drain (S/D) electrodes in a-IGZO TFTs. The devices demonstrated promising characteristics, on pair with TFTs using Al electrodes, with a threshold voltage (V _T) of -1.97 V, sub-threshold slope (SS) of 0.52 V/decade, saturation mobility (μ _sat) of 8.75 cm² V^-1 s^-1, and on/off current ratio (I _on/I _off) of 2.66 ×10⁸.