Thickness-dependent dielectric constants of (Ba,Sr)TiO3 thin films with Pt or conducting oxide electrodes

The decrease in the measured dielectric constant of sputter-deposited (Ba,Sr)TiO3 thin films having Pt electrodes with decreasing dielectric film thickness was analyzed by a combination of theories regarding the finite charge-screening length of the metal electrode and the intrinsic-dead layer of the dielectric surface. It was found that the decreasing dielectric constant was mainly due to the metal electrode capacitance rather than the intrinsic-dead-layer capacitance. The almost film-thickness-independent dielectric constant of the (Ba,Sr)TiO3 thin films with conducting oxide electrodes, IrO2 and SrRuO3, when the dielectric film thickness 20 nm, was attributed to the very high capacitance values of the charge-screening layer of the oxide electrodes. The very high capacitance value appeared to originate from the strain-induced high dielectric constant of the oxide electrodes.