Composition–phase structure relationship and thickness-dependent ferroelectricity of rhombohedral phase in [1 1 1]-textured Nb-doped Pb(Zr,Ti)O3 thin films

2% Nb-doped [1 1 1]-oriented lead zirconate titanate films (PNZT) of different Zr/Ti ratios ranging from 30/70 to 70/30 with a fixed thickness were deposited on the Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates by sol–gel method. The orientation degree, film morphology and phase transition of the PNZT films were investigated as a function of Zr/Ti ratios. The experimental results verified the composition-dependent phase transition from tetragonal to rhombohedral of the PNZT films with a visible [1 1 1] preferred orientation. To obtain high performance by making use of rhombohedrel [1 1 1]-oriented thin films, Pb(Zr0.6Ti0.4)Nb0.02O3 films with various thicknesses varying from 70 nm to 300 nm were studied to reveal the relationship among the film thickness, stress and ferroelectric response. It was found that ferroelectric property reached a high remnant polarization (Pr) of 61.7 μC/cm2 and a minimum coercive field (Ec) of 70.7 kV/cm at 300 nm due to the release of residual tensile stress.