AC conductivity and dielectric properties of sol-gel PZT thin films for ferroelectric memory applications

The dielectric properties and AC conductivity of sol-gel PZT (lead zirconate titanate) thin films were measured at frequencies between 10 and 10⁶ Hz and temperatures between 25°C and 500°C. At high frequencies e.g., >2 kHz, a maximum is observed in the real part of the complex dielectric constant, which corresponds to the Curie point. However, at low frequencies, e.g., 200 Hz, the dielectric constant increases monotonically with temperature. A space charge blocking model and an electric charge hopping model are discussed in order to explain this phenomenon. Further experimental results on the frequency dependence of dielectric constant and AC conductivity provide additional support for the charge hopping model. The AC conductance at high temperatures is much more sensitive to temperature than that at low temperatures. The activation energy Q₁ at high temperatures is about 1.3 eV. The apparent activation energy Q₂ at low temperatures is about 0.35 eV