Electrical characteristics of amorphous In-Ga-Zn-O thin-film transistors prepared by radio frequency magnetron sputtering with varying oxygen flows

This study investigates impacts of oxygen flow during the deposition of amorphous indium-gallium-zinc oxide (a-IGZO) channel layer with a radio frequency (r.f.) magnetron sputter on the electrical characteristics of the fabricated thin-film transistors (TFTs). Results indicate that as the film was deposited with a higher oxygen flow, the transfer curves are positively shifted while the field-effect mobility (μ_FE) is significantly decreased. To get more insight about the effects, channel resistance (R_CH) and the parasitic source-to-drain resistance (R_SD) of the fabricated devices are extracted using the total resistance method. The extracted a-IGZO channel resistance per unit length (r_ch) and R_SD are found to increase while the extracted effective mobility (μ_E) is decreased with increasing oxygen flow during sputtering. These observations are postulated to be related the decrease in the In/(In + Ga + Zn) ratio and the increase in the Zn/(In + Ga + Zn) ratio of the a-IGZO films with increasing the oxygen flow rate which lead to higher resistivity and lower carrier concentration. The extracted R_SD can be comparable with R _CH for the devices prepared with high oxygen flow, resulting in the roll-off of μ_FE as the channel length is shorter than 20 μm.