Investigation of thickness-dependent stress in PbTiO3 thin films

X-ray diffraction (XRD) and Raman spectroscopy were used to investigate stress dependence on thickness in PbTiO3 (PTO) films grown by pulsed liquid injection Metalorganic Chemical Vapor Deposition on a LaAlO3 (001) substrate (LAO). Films on sapphire substrate (R-plane) were used as polycrystalline film reference. Epitaxial PTO films with a dominant c-domain structure are grown on LAO substrate whereas the films on sapphire are polycrystalline. A detailed investigation of the PTO/LAO film microstructure by XRD gives evidence of PTO twinning. Both techniques reveal that PTO films are under tensile in-plane stresses. The study of the film thickness dependence of microstrains, grain size, volume fraction of a-domains as well as surface morphology of PTO/LAO films indicates that these parameters are clearly correlated. A change in the relaxation mechanism between 65 and 125 nm of film thickness has been evidenced. A c parameter gradient occurs throughout the film depth; it originates in stress relaxation due to a thickness increase. Raman spectra of PTO films allowed in-plane residual stress values to be estimated from the Raman shifts and are in good agreement with ha l-0 02 61 27 4, v er si on 1 6 M ar 2 00 8 Author manuscript, published in "Journal of Applied Physics 103 (2008) 014103" DOI : 10.1063/1.2821728