Electrophysical properties of lead zirconate titanate films doped with lanthanum

Abstract

The influence of lanthanum doping of lead zirconate titanate films (PZTL) on their polarization properties and leakage currents is studied. The films of Pb1 − x La x (Zr0.48Ti0.52)1 − x/4O3 with x = 0, 0.02, 0.05, 0.08, and 0.1 and a thickness of 240 nm were produced using the sol-gel method at an annealing temperature of 650°C on the substrates with a Si-SiO2-TiO2-Pt structure. It is found that the residual polarization and the coercive field are weakened after doping with La. The films with x = 0.02 exhibit satisfactory ferroelectric characteristics (7 μC/cm2, 25 kV/cm) that make them suitable for use in ferroelectric memory. The current-voltage curves of PZTL films have two characteristic regions. In weak fields (up to 80–90 kV/cm), the leakage current is attributable primarily to the high resistance of the depletion region of the reverse-biased Schottky barrier at the electrode-ferroelectric interface, and the leakage current is thus practically independent of the La content. When the threshold voltage is exceeded, the Schottky barrier breakdown occurs, and the leakage current in strong fields is defined by the density of free carriers in the bulk of the film. This density depends on the La doping level. The leakage current at x = 0.02 is reduced by about two orders of magnitude compared to undoped PZT film. Further increases in the La content are accompanied by an increase in the leakage current in strong fields. This effect is attributed to a change in the conduction type and an increase in the density of n-type carriers.