Sub-volt metal-oxide thin-film transistors enabled by solution-processed high-k Gd-doped HfO₂ dielectric films

Metal-oxide high-k dielectric films have received considerable attention in lowering the driving voltage and power consumption in semiconductor devices. Here, we demonstrate sub-volt operating metal-oxide thin-film transistors (TFTs) using solution-processed high-k gadolinium-doped hafnium oxide (HGO) dielectric films. Particularly, the HGO dielectric films were fabricated using a solution combustion synthesis (SCS) method using acetylacetone and 1,1,1-trifluoroacetylacetone as cofuels. The HGO dielectric films exhibited low leakage current of 2.7 × 10⁻⁶ A/cm² at 1 MV/cm and dielectric constant of ∼17. It was found that the Gd doping had a significant impact on improving the leakage current characteristics compared to the undoped HfO₂ films (leakage current of ∼10⁻² A/cm² at 1 MV/cm). By employing the high-k HGO gate dielectric layer, we demonstrated 0.5 V-operating indium-gallium-zinc-oxide TFTs exhibiting field-effect mobility of 3.55 cm²/Vs, on/off ratio of 5.9 × 10⁵, and subthreshold slope of 75 mV/decade. We investigated the effects of cofuel concentration on the film morphology and dielectric properties of HGO films to determine the optimal cofuel concentration for SCS. Furthermore, X-ray photoelectron spectroscopy was performed to reveal the role of Gd doping in improving the dielectric properties in correlation with the oxygen vacancy formation. Based on these results, we claim that the high-k HGO film fabricated through the SCS route can be a promising candidate for realizing sub-volt operating TFTs for low-power consumption.