Stress in Pt/Pb(Zr,Ti)O3/Pt capacitors for integrated ferroelectric devices

Stresses were studied in a ferroelectric capacitor consisting of Pt bottom and top electrodes and a Pb(Zr,Ti)O₃ (PZT) film during and after its processing. The Pt electrodes were deposited by sputtering. The PZT film was made by a sol-gel technique. Stress measurements after each deposition step, during annealing treatments and after etching steps made it possible to follow the stress evolution in the capacitor. The largest stress effects are found in the Pt-electrodes. After sputter-deposition these have a large intrinsic compressive stress which is changed into a large thermal tensile stress after a temperature treatment exceeding 500°C. The stress in the PZT film is small and is influenced by the deposition of the top electrode. An analysis shows that it is mainly of thermal nature. Thermal cycling shows that after the top electrode is annealed the as grown poling direction which has a large component in the plane of the substrate is changed to a poling direction perpendicular to the substrate. This results in a large improvement of the switching behavior of the PZT film