High performance of solution-processed SnO₂ thin-film transistors by promotion of photo-exposure time-dependent carrier transport during the pre-annealing stage

We fabricate high-performance solution-processed SnO₂ thin-film transistors (TFTs) exhibiting improved carrier transport features by exposing the ultraviolet/ozone (UV/O₃) on the SnO₂ film during the pre-annealing stage. The SnO₂ layer is treated with different UV/O₃-exposure times from 0 to 60 minutes before the post-annealing step. As UV/O₃-exposure time increases from 0 to 30 minutes, the M-O-M (M, metal; and O, oxygen) network, mass density, and oxygen vacancies of films are enhanced. In contrast, the M-O-M network and mass density decrease, while the oxygen vacancies rather increase when the UV/O₃-exposure time reaches 60 minutes beyond 30 minutes. The SnO₂ (Sn⁴⁺) phase, thickness, and surface morphology of SnO₂ films are not considerably changed regardless of UV/O₃-exposure time. When the UV/O₃-exposure time is 30 minutes, devices demonstrate superior field-effect mobility (10.1 cm² V^-1 s^-1) at approximately two times higher than the TFT without UV/O₃-exposure. Furthermore, the SnO₂ TFT with UV/O₃-exposure time for 30 minutes shows improved subthreshold-swing characteristics and a high on/off current ratio. These devices are adequate for use in high-resolution active-matrix LCDs or OLED displays that demand a high field-effect mobility (>10 cm² V^-1 s^-1) and on/off ratio (>10⁶).