Conspicuous voltage shift of D-E hysteresis loop and asymmetric depolarization in Pb-based ferroelectric thin films

Polycrystalline Pb(Zr,Ti)O-3 (PZT) thin films fabricated by a chemical solution deposition (CSD) process exhibited a conspicuous initial voltage shift in the D-E hysteresis loop toward the negative-bias field. It was concluded that the origin of the voltage shift was an internal bias field due to asymmetric space-charge distribution induced by the natural alignment of spontaneous polarization during the cooling process. The internal bias field also caused asymmetric depolarization at the zero-bias field. In heteroepitaxial (Pb,La)TiO3 thin films, we observed a conspicuous voltage shirt toward the positive-bias field and asymmetric depolarization at the zero-bias field. They were eliminated by the application of a positive unipolar pulse train.