Processing effects for integrated PZT: Residual stress, thickness, and dielectric properties

Processing effects on the dielectric properties of sol-gel-derived PbZrO ₃-PbTiO ₃ (PZT) films integrated onto Pt/Ti/SiO ₂//Si substrates are reported. Sol-gel synthesis and deposition conditions were designed to produce films of varying thickness (95-500 nm) with consistent chemical composition (Pb (Zr _0.53Ti _0.47)O ₃), phase content (perovskite), grain size (∼110 nm), crystallographic orientation (nominally (111) fiber textured), and measured residual stress. The Stoney method, using laser reflectance to determine wafer curvature, derived biaxial tensile stress values of 150 and 180 MPa for PZT films after a baseline correction for electrode interactions during thermal processing was employed. The PZT films were of high dielectric quality, with low losses and negligible dispersion. Calculated values of dielectric constant (K ^l) were found to decrease from 960 to 600 with decreasing film thickness. A series-capacitor model successfully recovered a room-temperature K′ ₁ for the PZT (1,170) in good agreement with bulk reports but was unable to reproduce the expected dielectric anomaly near 380°C. This discrepancy and the resulting diffuse phase transformation were attributed to the biaxial tensile stress present in the PZT films.