Stability Improvement of In-Sn-Ga-O Thin-Film Transistors at Low Annealing Temperatures

Thin-film transistors (TFTs) based on In-Sn-Ga-O (ITGO) semiconductors were evaluated with respect to different post-annealing temperatures (200 °C ~ 350 °C). High-performance devices were obtained, exhibiting field-effect mobility values exceeding 25 cm
²
/Vs at all thermal treatments. However, the threshold voltage shift (AV
_th
) under negative bias stress increased with increasing annealing temperature, which is opposite to what is generally observed in oxide semiconductor TFTs. It is suggested that annealing at elevated temperatures results in relatively large concentrations of oxygen deficient sites in ITGO. These defects act as sources of excess electron carriers, which induce large V
_th
shifts upon negative bias stress. Relatively low process temperatures are thus preferred in ITGO TFTs, which are anticipated to pave the way for the development of flexible displays.