One-Volt TiO₂ Thin Film Transistors With Low-Temperature Process

We report one-volt TiO2 thin film transistors (TFTs) with a low-temperature fabrication process. The TFTs with the 300 °C-annealed TiO2 channel exhibit a high on/off current ratio ( $\text{I}_{ \mathrm{\scriptscriptstyle ON}}/\text{I}_{ \mathrm{\scriptscriptstyle OFF}})$ of $5.4\times 10^{7}$ , a low subthreshold swing (SS) of 75 mV/dec and a saturation field effect mobility ( $\mu _{{\mathrm {sat}}}$ ) of 2.13 cm $^{2}\cdot V^{-1}\cdot s^{-1}$ under an ultra-low voltage of 1 V. In contrast, the TFTs with the 200 °C-annealed TiO2 channel show no appreciable currents. Such a distinct conductivity difference is attributed to the crystallinity transformation of stoichiometric TiO2, the charge transport of which can be well explained by the multiple-trapping-and-release (MTR) model. The channel/dielectric interfaces of these one-volt TiO2 TFTs are further investigated by transmission electron microscopy (TEM), multi-frequency ( ${f}$ ) capacitance-voltage (C-V), and conductance-voltage (G-V) measurements. The interface trap density ( $\text{D}_{{\mathrm {it}}}$ ) values of $\sim 5\times 10^{12}$ cm $^{-2}\cdot {\mathrm {eV}}^{-1}$ obtained from both C-V and G-V measurements are in good agreement, suggesting a high-quality channel/dielectric interface. These one-volt TiO2 TFTs show a great potential in emerging applications, such as foldable displays and wearable sensors, where a battery-powered operation is required.