Performance and Reliability of TiO 2/ZrO 2/TiO 2 (TZT) and AlO-Doped TZT MIM Capacitors

Metal-insulator-metal capacitors for dynamic random access memory applications have been realized using TiO₂/ZrO₂/TiO₂ (TZT) and AlO-doped TZT [TiO₂/ZrO₂/AlO/ ZrO₂/TiO₂ (TZAZT) and TiO₂/ZrO₂/AlO/ZrO₂/AlO/ZrO₂/TiO₂ (TZAZAZT)] dielectric stacks. High-capacitance densities of 46.6 fF/μm² (for TZT stacks), 46.2 fF/μm² (for TZAZT stacks), and 46.8 fF/μm² (for TZAZAZT stacks) have been achieved. Low leakage current densities of about 4.9 × 10^-8, 5.5 × 10^-9, and 9.7 × 10^-9 A/cm² (at -1 V) have been obtained for TZT, TZAZT, and TZAZAZT stacks, respectively. We analyze the leakage current mechanisms at different electric field regimes, and compute the trap levels. The effects of constant voltage stress on the device characteristics were studied, and excellent device reliability was demonstrated. The electrical characteristics of the devices were correlated with the structural analysis through X-ray diffraction measurements and the surface chemical states analysis through X-ray photoelectron spectroscopy measurements. The doped-dielectric stacks (AlO-doped TZT: TZAZT and TZAZAZT) help to reduce leakage current density and improve reliability, without substantial reduction in capacitance density, compared with their undoped counterparts (TZT).