Property engineering In BaTIO₃ films by stoichiometry control

BaTiO₃ thin films were prepared on metallic foil substratesusing chemical solution deposition. The Impact of A to B site cation ratioson the phase assemblage and microstructural and dielectric properties was investigated by characterizing a sample set that includes stoichiometric BaTiO₃ and 1, 2, 3, 4, and 5 mol% excess BaO. Each composition was subjected to a high-temperature anneal step with maximum dwell temperaturesof 1000, 1100, and 1200°C for 20 h. Excess barium concentrations greater than 3% lead to dramatic grain growth and average grain sizes exceeding 1pro. Despite the large deviations from stoichiometry and the 20 h dwell time at temperature, x-ray diffraction, and high-resolution electron microscopy analysis were unable to detect secondary phases until films with 5% excess barium were annealed to 1200°C. Thin films with 3% excess barium were prepared on copper substrates and annealed at 1060°C, the practical limit for copper. This combination of BaO excess and annealing temperature produced an average lateral grain size of 0.8 μn and a room-temperature permittivity of 4000. This is in comparison to a permittivity of 1800 for stoichiometric material prepared using identical conditions. This work suggests mctastablc solubility of BaO in BaTiO₃ that leads to enhanced grain growth and large permittivity values. This technique provides a new solid-state means of achieving grain growth in low thermal budget systems.