In this article, we evidence the lower formation energy and improved stability of the conductive filament (CF) formed in TiN\Ta 2 O 5 \Ta resistive-switching memory cells treated in NH 3 atmosphere at 400 C. This annealing treatment results in (i) lower forming voltage, (ii) lower CF resistance, and (iii) longer retention lifetime of the oxygen-vacancy (V o ) chain constituting the CF. Atomistic insights into these processes are provided by ab initio calculations performed for hydrogen (H) species incorporated in non-stoichiometric Ta 2 O 5 supercells: (i) V o formation energy is reduced by the presence of H, (ii) V o -chain CF conductivity is increased by V o þ OH complex formation, and (iii) V o -chain retention is strengthened by the stable V o þ OH complex. As a result, efficient CF formation and excellent state stability are obtained after 15 days at 250 C. V C 2015 AIP Publishing LLC.

The structures and electronic properties of Ta2O5 polymorphs were calculated using density-functional theory employing the generalized gradient approximation with on-site Coulomb corrections. Using this approach, a pseudo-hexagonal structure was found to be a stable polymorph of Ta2O5 over the 14δ' type="#_x0000_t75"> - and 14β' type="#_x0000_t75"> -Ta2O5 and is proposed as a new candidate structure which might be formed during the resistive switching process in random access memory devices. Its diffraction spectrum is shown to successfully match the recently indexed experimental structure and its band-gap energy is also in good agreement with available experimental data. A neutral oxygen vacancy is shown to induce an occupied defect state at 2.5 eV above the top of the valence band, as also found by x-ray photoelectron spectroscopy spectrum measurement. Furthermore, the effects of the hydrogen impurity on the electronic structures were investigated.