Improved tunable properties of Co doped Ba0.8Sr0.2TiO3 thin films prepared by sol-gel method

Ba0.8Sr0.2TiO3 thin films with different concentrations of Co dopant (0-10 mol%) were deposited on Pt/Ti/SiO2/Si substrates by sol-gel method. The microstructure, surface morphology, dielectric and tunable properties of the films were investigated as a function of Co concentration. It was demonstrated that all the Co doped Ba0.8Sr0.2TiO3 (BSTC) thin films exhibited dense microstructure with uniform crystal grains and the grain size of the BSTC films decreased with the increase of Co content. Both dielectric constant and loss decreased with the increase of Co dopant. It was proposed that the depressed dielectric loss in BSTC film originated from the reduction of intrinsic electrons by Co acceptor doping. Although tunability of the BSTC films was also reduced with the addition of Co dopant, a largest figure of merit of 4.5 was obtained in the BSTC film with 5 mol% Co dopant owing to the comparable tunability and low dielectric loss of the films, which made it an alternative source for potential tunable applications.