Solution-based flexible indium oxide thin-film transistors with high mobility and stability by selective surface modification

Improved performances of solution-based flexible indium oxide (In₂O₃) thin-film transistors (TFTs) was achieved by introducing clear-cut edges of the active areas on substrate surfaces. Patterned areas for the In₂O₃ active regions were converted to hydrophilic by oxygen plasma treatment whereas the remaining areas between the active region patterns were converted to hydrophobic by transferring oligomer molecules from a partially cured polydimethylsiloxane (PDMS) mask. This way, In₂O₃ precursor could be settled only on the intended patterns for the active regions and therefore the active regions were formed with distinct edges and regular shapes. A model TFT prepared via this method exhibited significantly improved performances over a reference device prepared without the selective surface treatment in terms of threshold voltage (V_th), subthreshold swing (SS), saturation mobility (μ_sat), off-state current (I_off), and bias-stress stability. Furthermore, the TFT exhibited good electrical stability under a bias stress and sustainable mechanical stability even at 10,000 cycles of bending tests at a radius of curvature of 5 mm. Such improvements were attributed to decreased trap state density at the channel/dielectric interface due to clear distinction of the active region edges and good interface properties, which also helped improving the mechanical stability under prolonged cyclic bending.