The Properties of Lead Titanate Thin Films produced by Chemical Vapour Deposition

Abstract

<p>This project focused on advancing the knowledge of chemical vapour<br />deposition (CVD) PbTiO₃ thin films for future work on lead zirconate titanate or PZT<br />(PbZrᵪT₁_ᵪO₃) through an understanding of the structural, chemical and electrical<br />properties of the material.</p> <p>A study of the individual oxides, TiO₂ and PbOᵪ, prepared also by CVD, was<br />made using transmission electron microscopy (TEM), scanning electron microscopy<br />(SEM), Raman spectroscopy and x-ray diffraction (XRD), before a low pressure, low<br />temperature process for PbTiO₃ was developed. The major factors in controlling the<br />film composition and thickness uniformity were identified. The formation sequence<br />for CVO PbTiO₃ films involved individual oxides of Ti and Pb, rather than<br />pyrochlore-type phases. A Pb-rich composition ensured the formation of perovskite,<br />however it resulted in the formation of a thin PbOᵪ surface layer. Removal of this<br />layer by etching gave improved electrical properties. Capacitance measurements<br />typically varied less than 1% over the frequency range and gave ε' values from<br />60-155. At 1 kHz, tan δ was ~0.01 and the resistivity was ~10¹¹Ω.cm.</p> <p>TEM examination of as-deposited films of PbTiO₃ revealed no macro-domains existed. After post-deposition annealing twinned structures acting as domains were<br />found in grains, ~0.1 μm in size. The origin of the theoretical minimum grain size<br />for twinning in PbTiO₃ thin films is discussed. A classification scheme for domain structures was developed based on thin films of PbTiO₃ and PZT. Similarities were<br />drawn between these domain structures and their bulk counterparts.</p> <p>The multi-layered bottom electrode of Pt and Ti used in this study was found<br />to react at temperatures ≤515°C. At higher temperatures (698°C), the Ti layer was<br />completely consumed, however the top surface of the Pt layer remained unaffected.</p>