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 $(\mathrm{Ba,Sr}){\mathrm{TiO}}_3$ 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 $(\mathrm{Ba,Sr}){\mathrm{TiO}}_3$ thin films with conducting oxide electrodes, ${\mathrm{IrO}}_2$ and ${\mathrm{SrRuO}}_3,$ 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.