Thermally Induced Variation of the Turn-ON Voltage of an Indium–Gallium–Zinc Oxide Thin-Film Transistor

The thermal processing of an indium-gallium-zinc oxide (IGZO) thin-film transistor (TFT) with annealing-induced source/drain (S/D) regions was found to induce a negative shift in the turn-ON voltage (VON) of the TFT. Such shifts are consistent with the presence of positive ions, and correlated with the detection of indium, gallium, and zinc, in the dielectric layer adjacent to the channel region. The origin of these species is attributed to the thermally induced dissociation of the IGZO in the S/D regions of the TFT, and the subsequent migration of some of the dissociated species to the dielectric layer above the channel region. It was found that the process-induced shifts in VON depended on not only the heat-treatment condition but also the structural configuration of the TFT. Since the thermal processes are practically unavoidable during the fabrication of an IGZO TFT and it is unlikely the dissociation of IGZO is unique to the present device architecture, attention must be paid to the effects of the potential migration of such ionic species on the device characteristics, regardless of the transistor structure.