Tuning dielectric properties of sputtered BaTiO3 thin film capacitors via multilayering with SrTiO3

BaTiO3/SrTiO3 (BTO/STO) multilayer films were successfully prepared on (La, Sr)CoO3-coated (100) SrTiO3 substrates by using a radio-frequency (RF) magnetron sputtering process at 700 degrees C. Benefiting from the flexible deposition configuration of a multi-target sputtering system, we were able to tune the dielectric properties of the multilayer film by varying the number of multilayer periods N and the individual layer thickness d. It was found that, in a superlattice-like structure (dBTO=dSTO=4 nm, similar to 10 unit cells), the dielectric constant increased and the loss tangent decreased with an increasing N, especially in the high frequency range (104-106 Hz). This can be attributed to a reduced volumetric contribution to the dielectric property from the leaky interface capacitor layer, which lies between the multilayer film and the (La, Sr)CoO3 electrode. On the other hand, as the individual layer thickness d exceeds the superlattice limit (dBTO=dSTO=8 nm, similar to 20 unit cells), the superlattice strain effect disappeared and the dielectric constant value dropped by similar to 50%. However, owing to the reduced number of interfaces and associated defects, the dielectric loss of the multilayer film with a larger period was reduced significantly, as compared to its superlattice counterpart with the same thickness and more periods. The dielectric loss power density of the former was about one order of magnitude lower than that of the latter. These observations provide a solid foundation for using RF magnetron sputtering as an effective method to prepare various forms of multilayer film capacitors for integrated device applications.