The properties of lead titanate thin films produced by chemical vapour deposition

Abstract

This project focused on advancing the knowledge of chemical vapour deposition (CVD) of lead titanate (PbTiO3) thin films for future work on lead zirconate titanate or PZT (PbZrxTi1−xO3) through an understanding of the structural, chemical, and electrical properties of the material. A low-pressure, low-temperature process for PbTiO3 was developed. The major factors in controlling the film composition and thickness uniformity were identified as substrate temperature and the partial pressures of the reactive gases. The formation sequence for CVD PbTiO3 films involved individual oxides of Ti and Pb, rather than pyrochlore-type phases. A Pb-rich composition ensured the formation of perovskite, however, it resulted in the formation of a thin PbOx surface layer. Removal of this layer by etching gave improved electrical properties. Capacitance measurements typically varied less than 1% over the frequency range and gave ε′ values from 60 to 155. At 1 kHz, tan ∂ was ~0.01 and the, resistivity was ~1011 Ω cm. Transmission electron microscopy examination of as-deposited films of PbTiO3 revealed no macrodomains existed. After post-deposition rapid thermal annealing (RTA), twinned structures, apparently acting as domains, were found in ~0.1 μm diameter grains. The multilayered bottom electrode of Pt and Ti used in this study was found to react at temperatures ≤ 515 °C. At higher RTA temperatures (698 °C), the Ti layer was completely consumed, however the top surface of the Pt layer remained unaffected.