Mesoscopic analysis of leakage current suppression in ZrO2/Al2O3/ZrO2 nano-laminates

Metal-Insulator-Metal capacitors, with ZrO2/Al2O3/ZrO2 (ZAZ)-nanolaminate thin-films as a dielectric layer, exhibit reduced leakage currents compared to corresponding capacitors based on pure ZrO2 while maintaining a sufficiently high dielectric constant for the DRAM application. This work is a comparative study demonstrating how the incorporation of a small amount of Al is responsible for the suppression of crystallization during deposition. Extensive electrical characterization leads to the identification of a defect band which conductive atomic force microscopy shows to be formed along crystallite grain boundaries, extending through the entire ZrO2-film. The incorporation of a sub-layer of Al2O3 prevents these grain boundaries resulting in an effective reduction of leakage currents, despite the film being in the nanocrystalline phase, necessary for it to exhibit the required high dielectric constant. A transport model based on phonon assisted trap to trap tunneling is proposed.