Amorphous In–Ga–Zn–O Dual-Gate TFTs: Current–Voltage Characteristics and Electrical Stress Instabilities

We studied the electrical characteristics and electrical stress instabilities of amorphous In-Ga-Zn-O (-IGZO) dual-gate thin-film-transistors (DG TFTs). A threshold voltage of the bottom-gate (BG)-driven -IGZO DG TFTs showed a linear dependence on the top-gate (TG) voltage. The slope of this dependence is associated with the ratio of the TG to BG insulator capacitance. The BG-driven DG TFT showed linear field-effect mobility comparable to that of a single-gate (SG) TFT without the TG electrode and a smaller saturation field-effect mobility and a larger subthreshold swing in comparison to the SG TFT. These characteristics were explained by the BG-driven DG TFT model formulated by taking the TG bias effect into account. The TG interface showed worse stability under an electric bias stress in comparison to the BG interface. It was also found that a negative voltage applied to the TG improved the stability of the DG TFT under a constant-current stress. These observations suggest that the BG-driven -IGZO DG TFTs with the appropriate negative TG voltage applied can simultaneously show both normally off characteristics and higher stability than the SG TFTs.