Solution Processed Hafnium Oxide Doped Siloxane Dielectrics for a Thin Film Transistor with Reduced Graphene Oxide Channel on Flexible Substrate

High-k materials for gate dielectric layers, such as hafnium oxide (HfO₂), have been developed for decades to increase the integration density of complementary-metal-oxide-semiconductor (cMOS) devices. In this study, we demonstrate a thin film transistor (TFT) device with solution processed non-stoichiometric hafnium oxide (HfO _x ) doped siloxane dielectric fabricated on a flexible polyethylene terephthalate (PET) substrate. The air-stable powder precursor of the HfO _x could be doped into the solution precursor of octamethylcyclotetrasiloxane (OMTS) with additional UV-ozone oxidation at a low temperature of 110 °C. The dielectric properties of the HfO _x doped siloxane films in metal-insulator-silicon (MIS) devices were investigated via capacitance–voltage (C–V ) measurements. The annealed dielectric layer with UV-ozone oxidation attained a high dielectric constant, and no hysteresis was detected in the C–V measurements. Two-dimensional (2D) carbon structure of reduced graphene oxide (rGO) was used for the active channel of the TFTs, because of its superior properties of fast electron transport and high chemical stability. The output and transfer characteristics of the rGO TFTs were investigated with the HfO _x siloxane dielectric. The simple low-temperature fabrication process proposed in this paper will advance further applications in transparent and flexible electronics.