Lanthanum Aluminum Oxide Thin-Film Dielectrics from Aqueous Solution

Amorphous LaAlO₃ dielectric thin films were fabricated via solution processing from inorganic nitrate precursors. Precursor solutions contained soluble oligomeric metal-hydroxyl and/or -oxo species as evidenced by dynamic light scattering (DLS) and Raman spectroscopy. Thin-film formation was characterized as a function of annealing temperature using Fourier transform infrared (FTIR), X-ray diffraction (XRD), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and an array of electrical measurements. Annealing temperatures ≥500 °C result in thin films with low leakage-current densities (∼1 × 10^–8 A·cm^–2) and dielectric constants ranging from 11.0 to 11.5. When incorporated as the gate dielectric layer in a-IGZO thin-film transistors (TFTs), LaAlO₃ thin films annealed at 600 °C in air yielded TFTs with relatively low average mobilities (∼4.5 cm²·V^–1·s^–1) and high turn-on voltages (∼26 V). Interestingly, reannealing the LaAlO₃ in 5%H₂/95%N₂ at 300 °C before deposition of a-IGZO channel layers resulted in TFTs with increased average mobilities (11.1 cm²·V^–1·s^–1) and lower turn-on voltages (∼6 V).