Water adsorption effects of nitrate ion coordinated Al2O3 dielectric for high performance metal-oxide thin-film transistor

Abstract

A solution-processed ionic amorphous Al₂O₃ dielectric with a low temperature annealing process at 350 °C shows good compatibility and high performance in metal oxide semiconductor thin film transitors (TFTs) such as Li–ZnO TFTs and In–ZnO TFTs. The Li–ZnO/Al₂O₃ and In–ZnO/Al₂O₃ TFTs, with solution-processability and low temperature annealing at a maximum of 350 °C, exhibited field-effect mobilities of 46.9 cm² V⁻¹ s⁻¹ in crystalline Li–ZnO/Al₂O₃ TFTs and 44.2 cm² V⁻¹ s⁻¹ in amorphous In–ZnO/Al₂O₃ TFTs with an on/off current ratio of more than 10⁵. The proton mobile ion, such as hydrogen ion (H⁺) from chemisorbed water, in the ionic Al₂O₃ dielectric remarkably induces a high performance capacitance by the formation of an electrical double layer. The chemisorbed water was monitored by FT-IR and ellipsometric porosimetry measurements. Furthermore, the addition of H₂O₂ to the ionic Al₂O₃ dielectric precursor successfully suppressed the oxygen vacancies in the dielectric layer, which caused the electrical trap and pass, and confirmed the stable operation. These ionic amorphous Al₂O₃ dielectrics show good potential as switching TFTs devices in advanced displays, because they can satisfy the various demands of next-generation high-performance TFTs, such as low-cost, solution-processability, and a relatively low-temperature process.