Microstructures and ferroelectric properties of barium strontium titanate thin films

Barium strontium titanate (BST) thin films were prepared by RF magnetron sputtering. The microstructures and ferroelectric properties of Ba0.6Sr0.4TiO3 thin films were investigated. The composition of BST thin film with tetragonal perovskite structure was near to that of the BST ceramic target. A 90 domain was observed by piezoresponse force microscopy (PFM). It is found that the critical size from a mufti-domain to a single-domain is from 28 nm to 33 nm. The dielectric constant-voltage curves and polarization hysteresis loops of BST thin films have been measured. At 1 kHz the dielectric constant, tunability and dielectric loss of the Ba0.6Sr0.4TiO3 film with thickness 280 nm are 562, 25.6% and 0.016, respectively. The remanent polarization (Pr) and the coercive electric field (Ec) of the BST film are 1.2 mu C/cm(2) and 42.9 kV/cm at room temperature, respectively. The epsilon(r)-V and P-V curves are asymmetric, and show a voltage shift toward the negative side, which may be caused by asymmetric potential barriers at the upper and bottom interfaces.