Enhancement-/Depletion-Mode TiO2 Thin-Film Transistors via O2/N2 Preannealing

Metal-oxide thin-film transistors (TFTs) promise to enable lightweight and low-power applications, such as ultrathin active matrix displays and low-cost RF identification tags. However, most reported high-performance metal-oxide TFTs contain high-cost indium and gallium elements, leading to constraints in cost-sensitive application. Herein, we present enhancement-/depletion-mode (E-/D-mode) TiO
₂
TFTs via
$\text{O}_{{2}}/\text{N}_{{2}}$
preannealing of TiO
₂
channel material prior to device fabrication process. It is found that the O
₂
-annealed TiO
₂
TFTs exhibit improved performances compared to N
₂
-annealed TiO
₂
TFTs, including increased mobility (
$\mu $
), higher ON-/OFF-current ratio (I
_ON
/I
_OFF
), and lower subthreshold swing (SS). This can be attributed to the passivation effects of O
₂
annealing, which leads to less oxygen vacancies at the channel and channel/oxide interface. On the other hand, the ionized oxygen vacancies result in the increased electron concentration in N
₂
-annealed films and, thus, the negative shift of
${V}_{\text {th}}$
in the TFT performance. This article delivers a possible approach to improve oxide TFT performance by passivation of oxygen vacancies. Furthermore, the controlled annealing process has a great potential in the logic inverter applications when both E- and D-mode TFTs are implemented.