Phase evolution and annealing effects on the electrical properties of Pb(Zr_0.53Ti_0.47)O₃ thin films with RuO₂ electrodes

The electrical properties and crystallization of Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films grown on RuO₂ electrodes by the sol-gel process have been studied. It was found that the amorphous as-deposited thin film first transforms to a pyrochlore phase at 500 °C. On further annealing, perovskite PZT begins to crystallize at about 600 °C. TEM anlysis reveals that a pyrochlore-type second phase still exists in the films even after annealing to temperatures of 750 °C for 10 min. These PZT films are fatigue-free, but they show large property variation and high leakage currents (J = 10^-3 A cm^-2 at 1 V). An 800 °C annealing treatment, for 10 min in air of the RuO₂ bottom electrode prior to film deposition enhanced perovskite PZT nucleation, thereby eliminating the pyrochlore-type second phase. In addition, the leakage currents of PZT films grown on annealed RuO₂ electrodes are about two orders of magnitude lower than those of PZT films grown on unannealed RuO₂. It is also observed that annealing the entire capacitor stack after the top electrode deposition improved capacitor properties.