Thermal study of multilayer resistive random access memories based on HfO2 and Al2O3 oxides

An in-depth analysis including both simulation and experimental characterization of resistive random access memories (RRAMs) with dielectric stacks composed of two layers of HfO2 and Al2O3 stacked in different orders is presented. The simulator, which includes the electrodes in the simulation domain, solves the 3D heat equation and calculates the device current. The results are employed to analyze thermal effects in bilayer HfO2 and Al2O3-based RRAMs with electrodes of Ni and Si-n+ during resistive switching (RS) operation. According to simulations and the experimental data, the narrow part of the conductive filaments (CF) is formed in the HfO2 layer in all the cases, and, therefore, no important differences are found in terms of reset voltage if the oxide stack order is changed with respect to the electrodes. This result is attributed to the fact that the heat flux in Al2O3 is higher than in the HfO2 layer and this determines the thermal behavior and RS operation. The heat transfer rate from the conductive filament to the electrodes and the surrounding oxide has been analyzed. The lateral heat flux component from the CF to the oxide is shown to be important with respect to the vertical component (from the CF to the electrodes).