Sol–gel derived Pb(Zr,Ti)O3 thin films: Residual stress and electrical properties

Pb(Zr,Ti)O3 compositions are under investigation for applications that include integrated capacitors, piezoelectric sensors, and actuators. Sol–gel synthesis and spin coating are popular routes to the formation of high quality, dense, crack free, insulating films. However, the electrical properties of the films are often different than those measured for bulk specimens of the same composition. Pb(Zr0.53Ti0.47)O3 films were deposited from a 2-methoxyethanol based sol–gel system onto Pt/Ti/SiO2//Si substrates via spin-casting. Multiple layers were sequentially deposited and heat-treated to 650 °C with the use of a PbO overcoat to ensure complete perovskite phase formation. Film thickness was varied from 0.19 to 0.5 μm to study the effect of thickness and residual stress on the dielectric and piezoelectric properties of the polarizable and deformable material. Ex-situ wafer curvature measurements, combined with cross-sectional scanning electron microscopy, allowed for the determination of residual stresses in the thin films calculated by the Stoney equation. The macroscopic boundary conditions were then related to the measured properties of interest, namely dielectric constant, tan δ, and piezoelectric strain coefficient. Measured dielectric constants varied from ∼750 to ∼1000, while d33 values ranged from 30 to 44 pm/V, as determined by single-beam heterodyne laser interferometry measurements.