Structures and Dielectric Properties of CeY Codoping Barium Strontium Titanate Films

Cerium (Ce) and Yttrium (Y) codoped Ba0.6Sr0.4TiO3 (BST) films have been prepared on Pt/Ti/SiO2/Si substrate by an improved sol-gel method. The structure and dielectric properties of the films have been studied. Scanning electron microscope (SEM) images show that codoping makes films compact and decreases shrinkage cavity, and the films have uniform grain size and become smoother with the increasing codoping concentration. Atomic force microscope (AFM) presents that codoped films show smooth surface with small roughness and small grain size with clear grain boundary with increasing codoping concentration. The V-C curves at 40 V and 100 kHz show that codoping improves the combination of dielectric properties. 2% Ce and 2% Y codoped BST thin film presents the best dielectric properties with capacitance 7.6x10(-11) F and dielectric loss (tan delta) 0.0126 at zero bias and tunability 41% and figure of merit 32.5 at 40 V, satisfying the needs of microwave tuned devices.