Low-Leakage and Low-Voltage Rare-Metal-Free TFTs Using Solution Combustion-Synthesized Al₂O₃ Dielectrics

Integrating high-κ dielectrics is essential for achieving low-voltage operation in cost-effective solution-processed thin-film transistors. However, solution-processed dielectrics often exhibit high leakage due to incomplete metal oxide stoichiometry and inherent film impurities. Here, we demonstrate a low-leakage and low-voltage Si _x Sn _y O TFT using a combustion-assisted Al₂O₃ dielectric. Previous reports on solution-processed Al₂O₃ thin films often faced challenges regarding film quality and dielectric performance, frequently exhibiting leakage currents in the microampere range. To overcome these issues, we established optimal parameters of Al₂O₃ preparation via solution combustion synthesis. Solution combustion synthesis is unique and beneficial because the exothermic heat of combustion promotes metal oxide formation, thereby improving the conventional sol-gel method for producing thin films. Through optimization, we confirmed that 0.10 M is the most suitable Al³⁺ concentration, producing films with good surface roughness and high bulk density. Additionally, stacking Al₂O₃ films via multilayer spin-coating yielded a denser film, resulting in a leakage current density of approximately 6.0 nA/cm² at 2.0 MV/cm and a breakdown field of approximately 3.6 MV/cm. Overall, the film produced using 0.10 M and 3 layers exhibited better quality with fewer trap states. Moreover, despite a thickness of approximately 30 nm, the leakage current rivals that of other vacuum-processed Al₂O₃ films. Using this dielectric, Si _x Sn _y O TFTs were fabricated and exhibited excellent TFT performance: μ_lin = 2.76 cm²/(V·s), V _ON = 0.27 V, I _ON/I _OFF = 3.4 × 10⁵, and SS = 0.23 V/dec.