The roles of B-site ions in lead strontium zirconate titanate thin films for electrically tunable device applications

B-site modification lead strontium zirconate titanate Pb_0.4Sr_0.6Zr_xTi_{1 - x}O₃ (PSZT, x = 0-0.7) thin films were prepared on Pt/TiO₂/SiO₂/Si substrates by a sol-gel method. The XRD results indicate that paraelectric PSZT thin films at room temperature are obtained as x approaches 0.2. The temperature-dependent dielectric and hysteresis loop measurements reveal that the thin films have diffuse phase transition characteristics and relaxor-like behavior with nano-polar regions in the paraelectric films at room temperature. The Curie temperature of the PSZT thin films varies with the Zr contents, exhibiting a complex trend. This can be attributed to two competitive factors: higher mobility of Ti⁴⁺ than Zr⁴⁺ and smaller open space left for the displacement of Ti ions with the increase of Zr content. The further increase of the Zr contents leads to the simultaneous decrease of dielectric constant, dielectric loss and tunability. PSZT (x = 0.4) thin film shows the largest figure of merit of 24.3 with a moderate tunability of 55.8% and a dielectric loss of 0.023. This suggests that B-site ions have different roles in modifying the electrically tunable performance of PSZT thin films for tunable microwave device applications.