Properties of PZT thin films as a function of in-plane biaxial stress

The properties of lead zirconate titanate (PZT) thin films were characterized as a function of in-plane biaxial stress. Typical values of P_r and E_c for unstressed (i.e. no applied load) sol-gel films were measured using Pt/PZT/Pt/Ti/SiO₂/Si test capacitors and are on the order of 28 μC/cm² and 63 kV/cm, respectively, Residual stresses in PZT/electrode stacks were found to be a function of the annealing condition for the Pt/Ti bottom electrode. Measured values of Pt/Ti stress for sputtered films consisting of 150 nm Pt and 20 nm Ti varied with temperature from -386 MPa in the as-received state to 718 MPa after heating to 700°C. Experimental stress states (of test capacitors) were modified from the fabricated condition in a biaxial stress rig designed to provide uniform tensile or compressive load over the surface of a 3" substrate. The resulting applied stress state in the films ranged from -142 MPa to 212 MPa. Remnant polarization, coercive field strengths, capacitance, and tan δ were then measured in situ and correlated to the state of stress in the PZT film