Properties and thermal stability of solution processed ultrathin, high-k bismuth titanate (Bi2Ti2O7) films

Ultrathin bismuth titanate films (Bi2Ti2O7, 5–25 nm) are deposited onto SiO2/Si substrates by aqueous chemical solution deposition and their evolution during annealing is studied. The films crystallize into a preferentially oriented, pure pyrochlore phase between 500 and 700 °C, depending on the film thickness and the total thermal budget. Crystallization causes a strong increase of surface roughness compared to amorphous films. An increase of the interfacial layer thickness is observed after anneal at 600 °C, together with intermixing of bismuth with the substrate as shown by TEM-EDX. The band gap was determined to be ∼3 eV from photoconductivity measurements and high dielectric constants between 30 and 130 were determined from capacitance voltage measurements, depending on the processing conditions.

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► Aqueous solution processed ultrathin Bi2Ti2O7 films below ∼20 nm thickness.
► Low temperature films are carbonate free, amorphous and have a high k value (33).
► High temperature allows crystallization and increases the k value (130).
► Crystallized films have higher roughness and thicker interfacial layers.
► Bismuth silicate is formed through interfacial reaction with the SiOx/Si substrate.