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

• Carrier concentration increased with reducing oxygen flow tends to enhance uFE, on-current; reduce Vth, SS.
• rch is higher while μE is lower in the films with a higher oxygen flow.
• Increasing O2 flow decreases In atom% and increases Zn atom% of IGZO films.
• Increasing O2 flow increases channel resistance and contact resistance.
• Visible decline in μFE as shorter channel length of devices with higher O2 flow.

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 (μFE) is significantly decreased. To get more insight about the effects, channel resistance (RCH) and the parasitic source-to-drain resistance (RSD) of the fabricated devices are extracted using the total resistance method. The extracted a-IGZO channel resistance per unit length (rch) and RSD are found to increase while the extracted effective mobility (μE) 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 RSD can be comparable with RCH for the devices prepared with high oxygen flow, resulting in the roll-off of μFE as the channel length is shorter than 20 μm.

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