This paper presents the results of I-V and constant-voltage-stress measurements on symmetrical dielectric ZrO₂/Al₂O ₃/ZrO₂ film stacks of different thicknesses. The films were grown by atomic layer deposition and structured into cylindrical metal-insulator-metal capacitors. The temperature-dependent leakage characteristics and time-dependent dielectric breakdown behaviors were investigated. A correlation was found between the structural composition, the defect density, and the conduction mechanism.