Residual stress analysis in ferroelectric Pb(Zr0.52Ti0.48)O3 thin films fabricated by a sol-gel process

Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) films were prepared by a modified sol-gel process, in which polyethylene glycol (PEG) was added to the precursor solutions. An x-ray diffraction (XRD) method that detected the d(123) variation associated with the change in the incline angle ψ of the plane (123) was developed to quantify the residual stress in the PZT films. The stress could not be determined from the wafer curvature due to the effects of both the underlying layers and interdiffusion among layers. Using our XRD method, it was found that the residual stress in the resulting PZT films was significantly reduced when PEG was added to the precursor solutions. Moreover, we observed a further reduction of residual stress with increasing molecular weight of the PEG additive. These results could explain why a thicker, crack-free film can be achieved by adding polymers to the sol-gel precursor solutions.