Enhanced dielectric and tunable characteristics of K-doped Ba0.5Sr0.5TiO3 thin films prepared by pulsed laser deposition

A series of potassium-doped barium strontium titanate ((Ba0.5Sr0.5)1−xKxTiO3) targets with dopant concentration (x) from 0 to 12.5mol% were synthesized by solid state reaction and the corresponding thin films were fabricated on (111) Pt/Ti/SiO2/Si substrate by using pulsed laser deposition. The doping of K shows strong influences on structural, dielectric and tunable characteristics. Surface roughness of the films decreases with the doping of K up to 7.5mol% and then increases with further increase of K, whereas the grain size is found to be minimum at 7.5% K. The maximum values of tunability and figure of merit obtained for the optimum 7.5mol%K-doped thin films are 77% and 65 at an applied field of 400kV/cm at 100kHz, respectively, which corresponds to significant improvements compared to the reported results processed by sol–gel or sputtering. The relaxation of crystalline strain inside the grains, and smoother surface with smaller grains are assumed to be responsible for the improved tunability and lower dielectric loss. ► Potassium-doped BaSrTiO3 films prepared by pulsed laser deposition ► Excellent tunability of 77% and figure of merit of 65 at 400kVcm−1 ► Strong dependence of K-doping level on dielectric and tunable characteristics ► Potential correlations to grain size, strain and surface roughness