High Performance Flexible Organic Thin Film Transistors (OTFTs) with Octadecyltrichlorsilane/Al₂O₃/Poly(4-vinylphenol) Multilayer Insulators

The incorporation of a thin, atomic layer deposited Al₂O₃ layer in between a spin-coated poly-4-vinyl phenol (PVP) organic layer and octadecyltrichlorsilane (OTS) in the multilayer gate dielectric for pentacene organic thin film transistors on a n⁺-Si substrate reduced the gate leakage current and thereby significantly enhanced the current on/off ratio up to 2.8 × 10⁶. Addition of the OTS monolayer on the UV-treated Al₂O₃ improved the crystallinity of the pentacene layer, where the OTS/UV-treated Al₂O₃ surfaces increased their contact angles to 100°. X-ray diffraction (XRD) analysis revealed a more intense (001) crystal reflectance of pentacene deposited on OTS/UV-treated Al₂O₃ surface than that on OTS/Al₂O₃ surface. Moreover, the improved pentacene layer contributed to the field effect mobility (0.4 cm²/Vs) and subsequently improved the electrical performances of organic thin film transistor (OTFT) devices. This PVP/UV treated Al₂O₃/OTS multilayer gate dielectric stack was superior to those of the device with the single PVP gate dielectrics due to the improved crystallinity of pentacene.