Self-polarization in PZT films

Sol-gel derived lead zirconate titanate (PbZr 0.4 Ti 0.6 O 3 , PZT) films of thickness 2 μm were spin-coated on RuO 2 /SiO 2 /Si substrates. A RuO 2 top electrode was then deposited on the PZT film by reactive rfmagnetron sputtering. X-ray diffraction studies reveal that the c-axis of the crystallites in the PZT film lies preferably in the plane of the film before the deposition of the RuO 2 top electrode. However, after the deposition of the RuO 2 top electrode, the c-axis of a large number of crystallites becomes normal to the plane of the film, thus leading to a large initial polarization (self-polarization) in the PZT film. The room-temperature pyroelectric coefficient of the PZT film is about 230 μC/m 2 K, and a large internal field of 40 kV/cm is also observed. We suggest that the PZT film is self-polarized by the internal field which is induced by the high-energy ion bombardment on the film surface during the rf-sputtering process.