A flexible amorphous Bi ₅Nb ₃O ₁₅ Film for the gate insulator of the low-voltage operating pentacene thin-film transistor fabricated at room temperature

The amorphous Bi ₅Nb ₃O ₁₅ film grown at room temperature under an oxygen-plasma sputtering ambient (BNRT-O ₂ film) has a hydrophobic surface with a surface energy of 35.6 mJ m ^-2, which is close to that of the orthorhombic pentacene (38 mJ m ^-2), resulting in the formation of a good pentacene layer without the introduction of an additional polymer layer. This film was very flexible, maintaining a high capacitance of 145 nF cm ^-2 during and after 105 bending cycles with a small curvature radius of 7.5 mm. This film was optically transparent. Furthermore, the flexible, pentacenebased, organic thin-film transistors (OTFTs) fabricated on the poly(ether sulfone) substrate at room temperature using a BNRT-O2 film as a gate insulator exhibited a promising device performance with a high field effect mobility of 0.5 cm ² V ^-1 s _-1, an on/off current modulation of 105, and a small subthreshold slope of 0.2 V decade ^-1 under a low operating voltage of -5 V. This device also maintained a high carrier mobility of 0.45 cm ² V ^-1 s ^-1 during the bending with a small curvature radius of 9 mm. Therefore, the BNRT-O ₂ film is considered a promising material for the gate insulator of the flexible, pentacene-based OTF