Structure and Electrical Properties of Zirconium-Aluminum-Oxide Films Engineered by Atomic Layer Deposition

Abstract

Thin films containing either multilayer ZrO2:Al2O3 structures or ZrO2 deposited on ZrxAlyOz buffer layers were characterized. The films were grown by atomic layer deposition (ALD) at 300 °C from ZrCl4, Al(CH3)3, and H2O. The multilayer ZrO2:Al2O3 structures were grown repeating different combinations of ZrO2 and Al2O3 ALD cycles while the ZrxAlyOz layers were obtained in a novel process using ALD cycles based on successive adsorption of ZrCl4 and Al(CH3)3, followed by surface reaction with H2O. The films were grown on TiN electrodes, and supplied with Ti top electrodes, whereby ZrxAlyOz films were exploited as thin buffer layers between TiN and ZrO2. The as-deposited ZrO2 films and ZrO2:Al2O3 structures with sufficiently low concentrations of Al2O3 were crystallized in the form of cubic or tetragonal ZrO2 polymorph possessing relative permittivities reaching 35. Notably, multilayered ZrO2:Al2O3 films could exhibit resistive switching behavior with ratios between low- and high-resistive-state current values, extending up to five orders of magnitude. Implications of multilevel switching were recorded. In the double-layered ZrxAlyOz-ZrO2 stacks, the ON/OFF current ratios remained below 40, but the endurance could become extended over 3000 cycles. Remarkably, instabilities, when detected in endurance behavior expressed by reduction in an ON/OFF current ratio could be compensated and the current values restored by real time readjustment of the programming voltage amplitude.