Molecular design of improved precursors for the MOCVD of electroceramic oxides

Metalorganic chemical vapour deposition (MOCVD) is a highly promising technique for the deposition of dielectric and ferroelectric oxide thin films such as TiO2, ZrO2, HfO2, Pb(Zr,Ti)O-3, SrBi2Ta2O9 and Pb(Sc0.5Ta0.5)O-3 which have a variety of applications in electronic devices. A key requirement in this technology is the availability of precursors with appropriate physical properties and decomposition characteristics, but there are problems associated with many of the existing precursors. Therefore, in order to exploit the full potential of MOCVD it is sometimes necessary to "tailor'' the properties of the precursor in order to optimise process parameters such as evaporation temperature, deposition temperature, layer purity and uniformity. In this paper the molecular design of a number of new oxide precursors is described, illustrating how the replacement of simple alkoxide groups by other groups, such as donor-functionalised alkoxide or beta-diketonate ligands, can result in precursors with improved physical properties and enhanced MOCVD performance.