Design, Preparation and Dielectric Properties of Excellent Yttrium-Doped Ba0.6Sr0.4TiO3 Films

Yttrium (Y)-doped barium strontium titanate ((Ba0.6Sr0.4)(x)TiO3, x<1, Y-BST) films and undoped BST films have been designed in terms of (Ba+Sr)/Ti atomic mol ratio, Y doped concentration and film thickness and prepared on Pt/Ti/SiO2/Si wafers by an improved sol-gel method, and the structures and dielectric properties of the films have been studied. X-ray diffraction (XRD) shows that all films exhibit cubic perovskite structures and mainly grow along (110) orientation. With the increase of (Ba+Sr)/Ti ratio (<1) or film thickness, the intensities of perovskite structures and the crystallization of films increase, but with the increase of Y doped concentration (>1% mol ratio), they weaken. 8-layer Y-BST film with (Ba+Sr)/Ti ratio of 0.9 and doped concentration of 2% mol ratio reveals smooth and dense structure with about 30 nm grain size and excellent combination of dielectric properties with capacitance of 18 pF (permittivity of 137) and dielectric loss of less than 0.01 at 0 V, and tunability of 46% and figure of merit of 77 at 40 V, meeting the needs of microwave applications. Related mechanisms were also presented.