Diffusion of oxygen in amorphous tantalum oxide

Abstract

The switching in resistive random-access memory (RRAM) relies on the migration of ions in sputtered amorphous transition metal oxides to both create and annihilate conductive filaments. A comprehensive understanding of ionic diffusion in these materials is therefore critical for optimizing future RRAM devices. While predicting diffusion barriers in crystalline materials is straightforward, the complex energy landscape in disordered materials makes analysis of the effective diffusion barrier inherently more difficult. Using classical molecular dynamics, we examine oxygen diffusion at various temperatures in amorphous tantala $({\mathrm{Ta}}_{2}{\mathrm{O}}_{5})$, a leading material for RRAM applications. We compare the predicted activation energies for self-diffusion to those from isotope tracer diffusion experiments. We find a diffusion activation energy of 1.55--1.60 eV, which is higher than that measured in isotopic diffusion experiments $(1.2\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$ on amorphous ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$. However, the predicted values are comparable to the activation energy $(1.60\ifmmode\pm\else\textpm\fi{}0.18\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$ determined from secondary ion mass spectroscopy analysis of isotopic diffusion experiments of sintered L-${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$ samples. We find that this difference could be due to issues of deposited film porosity, film stoichiometry, or else a preference for the empirical potentials to form nanocrystalline regions.