High-performance a-ITZO TFTs with high bias stability enabled by self-aligned passivation using a-GaOx

Abstract

Maintaining gate bias stability under negative bias stress (NBS) and positive bias stress (PBS) is a long-standing issue in amorphous oxide semiconductor thin-film transistors (TFTs). The passivation of the channel layer is crucial for improving device stability. We show that amorphous gallium oxide, which possesses appropriate energy levels (lower electron affinity and higher ionization potential) for indium–tin–zinc oxide (ITZO) TFTs, can be etched selectively by tetramethyl ammonium hydroxide-containing developers that enable self-alignment passivation, such as easy contact hole formation during the drain and source lithography processes. The self-aligned passivation process led to a-ITZO TFTs with high mobility (>50 cm2 V−1 s−1) and low subthreshold swing (<90 mV/dec). The threshold voltage shifts under NBS and PBS using a bias gate voltage of ±20 V for 1 h were −0.09 and 0.15 V, respectively. This passivation can obviate the need for the conventional CVD-derived passivation process by utilizing the DC sputtering of gallium oxide, which may reduce hydrogen issues.