Solution-Processed High-k HfO2 Gate Insulator for High-Performance Indium-Zinc-Oxide Thin-Film Transistors: Optimisation of Annealing Temperature and Insulator Thickness

HighlightsSystematic elucidation of annealing-temperature-dependent evolution of oxygen vacancies, M–O network densification, and crystallisation behaviour in sol–gel HfO2, directly correlating with TFT electrical performance and band alignment.All-solution-processed HfO2high-K gate insulator and IZO active layer are achieved via the sol–gel method, eliminating expensive vacuum equipment.The optimised 85 nm HfO2insulator annealed at 400 °C delivers outstanding device metrics (Ion/off= 1.11 × 106, SS = 0.53 V/dec, Vth = −1.1 V), proving that solution-derived HfO2is a viable and scalable alternative to conventional SiO2for TFT miniaturisation without performance trade-off.With the continuous advancement of display technology and advanced integrated circuits, oxide thin-film transistors (TFTs) have become core devices due to their high mobility, low leakage current and excellent large-area uniformity. To achieve low power consumption, high performance and high reliability, the introduction of high-k gate insulating layers is crucial. Among the numerous high-k materials, hafnium oxide (HfO2) has attracted significant attention due to its excellent dielectric properties and good compatibility with CMOS processes. In this paper, uniform and dense HfO2films were successfully fabricated using the sol–gel method to serve as insulating layers for TFT devices. Through experimental analysis, 400 °C was determined to be the optimal annealing temperature. At this temperature, the effects of replacing SiO2with HfO2as the insulating layer, as well as the impact of reducing film thickness, on TFT devices were investigated. Ultimately, at an annealing temperature of 400 °C, an 85 nm-thick HfO2film achieved the highest on/off current ratio (Ion/off= 1.11 × 106), the lowest subthreshold swing (SS = 0.53 V/dec), the lowest threshold voltage (Vth = −1.1 V) and the lowest off-current ratio (Ioff= 2.5 × 10−12A). It was confirmed that replacing SiO2with HfO2as the insulating layer is a viable approach for reducing the volume of TFT devices.