Dependence of dielectric and piezoelectric properties on film thickness for highly (100)-oriented lead magnesium niobate–lead titanate (70/30) thin films

Fiber textured (100)-oriented lead magnesium niobate-lead titanate (PMN-PT) (70/30) films with thicknesses between 0.35 and 2.1 μm were prepared using chemical solution processing. The degree of preferred orientation changed little with increasing thickness. However, the measured dielectric constant, remanent polarization, and piezoelectric coefficients (d₃₁) increased with increasing film thickness. The effective d₃₁ coefficients of highly (100)-oriented PMN-PT films on Pt-coated Si substrates were found to range from -16 to -96 pC/N. Ultraviolet illumination during poling resulted in abnormal aging behaviors and lower overall aging rates for the films. The initial nonlinear aging behavior was attributed to the presence of an internal space-charge field that developed from photoinduced charge carriers. As the space-charge field decays over time, the magnitude of d₃₁ increased until 450-500 min after poling, at which time d₃₁ remained either constant or declined slightly. Thus, the changes in d₃₁ were limited to 1-2%/decade 500-600 min after poling.