Structure and properties of PZT thin films on strontium ruthenate and calcium ruthenate electrodes

PZT thin films have been prepared via metalorganic CVD (MOCVD) on four substrates of conducting oxides of ruthenates, SrRuO3/Pt/Ti/SiO2/Si(1 0 0), SrRuO3/SiO2/Si(1 0 0), CaRuO3/Pt/Ti/SiO2/Si(1 0 0), CaRuO3/SiO2/Si(1 0 0). The conducting ruthenate layers were also grown using MOCVD. Ferroelectric properties of polarization fatigue and leakage current density are measured. The internal strain of PZT thin crystal which is mainly constrained by the bottom electrode seems to be the decisive factor in ferroelectric properties. The internal strain of PZT is represented by its tetragonality ratio. The PZT thin film in the capacitor Au/PZT/SrRuO3/Pt/Ti/SiO2/Si, with the largest tetragonality ratio 1.026, exhibits an optimum combination of large polarization, less fatigue, and low leakage current density. Both SrRuO3 and CaRuO3 are good diffusion barriers to prevent interdiffusion of cations between the ferroelectric and the electrode. The slightly higher intermixing at the CaRuO3-to-Pt/Ti interface is owing to the high annealing temperature needed in CaRuO3 synthesis.