Effect of (Ba + Sr/Ti) ratio on the dielectric properties for highly (111) oriented (Ba,Sr)TiO3 thin films

The (1 1 1) oriented barium strontium titanate (BST) thin films have been fabricated at 600 deg C on platinized Si substrates by RF-magnetron sputtering deposition at various deposition pressures. The crystal structure, surface morphology, and interface of the thin films have been characterized by XRD, FE-SEM, and TEM, respectively. Ba/Sr and (Ba + Sr)/Ti atomic ratios of the films are investigated by inductively coupled plasma spectroscopy. It is found that the dielectric constant and tunability of the obtained films considerably depend on the (Ba + Sr)/Ti ratio. The near-stoichiometry (4% Ti rich) film exhibits a highest dielectric constant and maximum tunability of 682 and 49%, respectively. The large off-stoichiometry film prepared at 20 mTorr has lowest losses (0.0064).