Enhancement of p-Type SnO Thin-Film Transistors via Self-Assembled Monolayers as Passivation and Interfacial Modification

This study systematically investigates three self-assembled monolayers (SAMs)─3-Aminopropyltriethoxysilane (APTES), octadecyltrichlorosilane (ODTS), and perfluorodecyltrichlorosilane (FDTS)─as surface passivation (Pa) and interfacial modification/surface passivation (In and Pa) layers to enhance the performance of p-type SnO thin-film transistors (TFTs). Structural and electrical characterization indicates that the SAM passivation suppresses surface-related trap states, leading to significant improvements in field-effect hole mobility (μ), on/off current ratio ( I on/off ), and threshold voltage ( V TH ) reliability. Specifically, APTES passivation yields a 154% increase in mobility, while FDTS passivation reduces the subthreshold swing by 35% and enhances the I on/off by more than 3.6-fold. When SAMs are further introduced at the channel/source/drain–electrode interfaces, their intrinsic surface polarity modulates interfacial charge distribution and contact properties, thereby tailoring the output and transfer characteristics of SnO TFTs. Notably, FDTS insertion enhances the output current and further increases μ by approximately 33.3% compared with FDTS passivation alone, whereas insertions of APTES and ODTS both with molecular dipole moments in opposite direction compared with FDTS tend to reduce the current. In addition, selected SAMs suppress gate leakage and enhance bias-stress reliability, both APTES and FDTS suppress V TH shifts under a +30 V bias, with FDTS insertion reducing Δ V TH from 5.41 to 4.39 V after 3600 s. These results demonstrate an effective and versatile surface and interface engineering strategy for substantially improving the performance and stability of p-type oxide TFTs.