Ferroelectric properties of Pb_xSr_1-xTiO₃ and its compositionally graded thin films grown on the highly oriented LaNiO₃ buffered Pt/Ti/SiO₂/Si substrates

Thin films of ferroelectric Pb_xSr_1-xTiO₃ (PST) with x=0.3-0.7 and graded composition were fabricated on LaNiO₃ buffered Pt/Ti/SiO₂/Si substrates by a sol-gel deposition method. The thin films crystallized into a single perovskite structure and exhibited highly (100) preferred orientation after postdeposition annealing at 650°C. The grain size of PST thin films systematically decreased with the increase of Sr content. Dielectric and ferroelectric properties were investigated as a function of temperature, frequency, and dc applied field. Pb _0.6Sr_0.4TiO₃ films showed a dominant voltage dependence of dielectric constant with a high tunability in a temperature range of 25-230°C. The compositionally graded PST thin films with x=0.3-0.6 also showed the high tunability. The graded thin films exhibited a diffused phase transition accompanied by a diffused peak in the temperature variations of dielectric constants. This kind of thin films has a potential in a fabrication of a temperature stable tunable device.