Investigation of HfO2 and ZrO2 for Resistive Random Access Memory applications

This work is focused on the investigation of Au/high k/TiN stacks for Resistive Random Access Memories. A screening of high k oxides, commonly used in advanced metal gates, such as HfO2 and ZrO2, is proposed. These oxides were grown on TiN electrodes using Atomic Layer Deposition and Plasma Enhanced Atomic Layer Deposition. The morphological and structural properties of the films were studied as a function of deposition temperature, film thickness and/or annealing using Atomic Force Microscopy, Grazing Incidence X-ray Diffraction and Attenuated Total Reflectance. An amorphous to crystalline transformation was observed with thickness for HfO2 and ZrO2, with deposition temperature for HfO2 from 300 to 350 degrees C, and with annealing in N-2 for 1 h at 400 degrees C for ZrO2. According to density measurements obtained using X-ray Reflectometry, HfO2 and ZrO2 are suspected to be stoichiometric whatever the thickness. The film stoichiometry was confirmed using X-ray Spectroscopy. Current-voltage measurements were performed on Au/high k/TiN, where Au and TiN are top and bottom electrodes, respectively. Whatever the high k material, the crystallization increases with thickness or/and temperature without any significant modification of the SET operation. The film annealing, which was proposed as an alternative way to crystallize ZrO2, may cause a modification of the interfaces, leading to a decrease of the switching performance. (C) 2012 Elsevier B.V. All rights reserved.