Characterization of rf-sputtered BaTiO3 thin films using a liquid electrolyte for the top contact

Abstract

BaTiO3 films 0.5 to 2.5 μm thick have been deposited by rf sputtering onto Pt substrates held at temperatures from 340 to 930 °C. The effects on the structure and electrical properties of deposited films annealed in air at temperatures of 935 and 1200 °C were determined. Film structure was characterized by x-ray diffraction and scanning electron microscopy. The electrical properties were measured using a liquid electrolyte for the top contact. Well-defined crystalline films of BaTiO3 were obtained only when the film was annealed at 1200 °C. Milder conditions resulted in amorphous structures and/or other crystalline stoichiometric compounds of barium titanate. The amorphous films were more coherent than the annealed structures, giving lower leakage currents but smaller dielectric constants of <300. Annealing the films raised the effective dielectric constant to values as high as 7000, with an accompanying decrease in the insulation resistance. The results are interpreted on the basis of formation of a porous, incoherent crystalline structure in the annealed films which have exposed areas of the Pt substrate in contact with the electrolyte.