Designing the thermal processing of Ba(Ti0.8Zr0.2)O3–(Ba0.7Ca0.3)TiO3 thin films from an ethylene glycol-derived precursor

Abstract

Lead-free ferroelectric 0.5Ba(Ti_0.8Zr_0.2)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BZT–BCT) thin films on platinized silicon substrates are prepared by a chemical solution deposition route. The solution chemistry involves the use of ethylene glycol and ethanol as solvents for alkaline earth acetates and transition metal alkoxides, respectively. The thermal decomposition of the BZT–BCT xerogel, the crystallization process of BZT–BCT thin films, and their homogeneity are investigated. In the xerogel, the decomposition of the organic residues occurs between 290 °C and 514 °C, followed by the formation of carbonate groups and their decomposition between 580 °C and 775 °C. In the thin films, the sequence of drying and pyrolysis steps, and the concentration of the coating solution influence the formation of carbonate groups and their decomposition upon annealing. Extending the drying and pyrolysis times from 2 minutes to 15 minutes and lowering the concentration of the coating solution from 0.2 M to 0.1 M contribute to an easier thermal decomposition of the carbon residues. Time-of-flight secondary ion mass spectrometry analysis reveals that upon rapid thermal annealing, the decomposition of the carbonate residues in a few tens of nanometres thick BZT–BCT film proceeds from the top downwards, resulting in a pure perovskite phase faster in the thinner films than in thicker ones. The about 100 nm thick BZT–BCT film annealed at 850 °C exhibits a columnar microstructure with a homogeneous distribution of elements across the thickness of the film.