Development of residual stress in sol-gel derived Pb(Zr,Ti)O3 films: An experimental study

Abstract

Residual stresses develop in the sol-gel-derived ferroelectric thin films during the transformation of the metal-organic gel to the metal oxide upon thermal treatment and due to the thermal and elastic mismatch between the Pb(Zrx,Ti1−x)O3 (PZT) film and the substrate materials during cooling. In this study, residual stresses were determined using the wafer curvature method after the deposition of multilayer PZT film on platinized (100) silicon wafers. A multilayer model for stress analysis was used to calculate the residual stress in PZT films of three different compositions: x=0.4, x=0.52, and x=0.6. Orientation dependent residual stresses were found in compositions containing the tetragonal phase, with x=0.4 and x=0.52. Depending on the fraction of (100) orientated domains low compressive or low tensile stress was found in Pb(Zr0.4Ti0.6)O3 (PZT 40∕60). Higher residual stress was found in PZT films consisting of only rhombohedral crystallographic structure (PZT 60∕40) while the residual stress in PZT films with morphotropic boundary composition (PZT 52∕48) was significantly dependent on the film orientation and the phase composition and could range from 17to90MPa. The effect of the film orientation on residual stress was found to be a function of the anisotropic thermal expansion coefficient of PZT. The contribution of the thermal and elastic properties of materials to the total wafer curvature was investigated and discussed. Finally, the residual stress results calculated with the four layer model were compared to the results calculated using the Stoney equation.