Stress effects in sol-gel derived ferroelectric thin films

Abstract

Residual stress development during processing of sol-gel derived ferroelectric thin films influences electromechanical properties and performance. The present work investigates the effects of stress on field-induced polarization switching in ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) (52/48) thin films. Film response is measured as a function of externally applied mechanical stress using a double-beam laser-Doppler heterodyne interferometer. This apparatus successfully eliminates any displacement contribution from flexural vibration of the substrate and enables measurement of the strain-electric field hysteresis loops as a function of applied stress. The field-induced strain in the PZT film increases with increasing compressive stress, while the opposite trend is observed for applied tensile stress. The dependence of electromechanical response on the external stress is attributed to the initial tensile residual stress state in the film. Tensile stress creates an in-plane clamping effect on the domains in the film, hindering polarization switching. The application of a compressive stress reduces tensile residual stress in the film and the constraint on the domains, leading to higher field-induced strains. Applied tensile stress amplifies the clamping effect, leading to lower field-induced strains.