First principles study of oxygen vacancy activation energy barrier in zirconia-based resistive memory

Abstract

Unlike experimental measurements that appeared to be quite large activation barriers, oxygen vacancies in zirconia-based resistive random access memory (ReRAM) are believed to migrate with a fairly low energy barrier, and this discrepancy has not been noticed nor seriously questioned up to date. In this paper, we work on this problem by means of first-principles calculations categorizing all the possible migration pathways by crystallographic directions. From the results, it is found that the low activation energy of oxygen vacancy that is expected from the switching characteristic of the device is originated from +2q charged oxygen vacancies in a nanometer-sized filament migrating into a particular crystallographic direction of monoclinic zirconia.

Kinetics of ion migration in the electric field-driven manipulation of magnetic anisotropy of Pt/Co/oxide multilayers

“…The small difference (with respect to the enthalpy of formation of Co oxide) between the barriers for positive and negative bias voltages, leads us to propose that the switching time is limited by the barrier associated to ionic migration in ZrO 2 . The value of U A ≈1 eV obtained in this work is of the same order of magnitude of that recently calculated for oxygen ion migration via oxygen vacancies in monoclinic ZrO 2 [25]. The lower activation barrier, compared to experimental values found in the literature (≈ 2 eV) may be associated to the amorphous sub-stoichiometric nature of our oxide, which was grown by ALD at low temperature to avoid deteriorating the magnetic properties of the magnetic stacks.…”

Exploring the direction-dependency of conductive filament formation and oxygen vacancy migration behaviors in HfO2-based RRAM

“…Blanka Magyari-Ko ¨pe et al 45 explored the effect of V O ordering in different directions on the electronic structure of rutile TiO 2 and NiO using firstprinciples calculations, and they found that the ordered oxygen vacancy CFs induced several defect states within the band gap, and such states may be responsible for the experimentally observed ''LRS''-state low resistance conduction. Ji-Hyun Hur 46 investigated the migration behaviors by crystallographic directions of V O in ZrO 2 -based RRAM and found that the V O with the charge states of +2q migrating along a particular crystallographic direction has the lowest V O activation energy. Therefore, a comprehensive and systematic investigation of these two issues would contribute significantly to revealing the resistive switching mechanisms of HfO 2 -based RRAM.…”

Defects in ferroelectric HfO2

“…The activation energy E a for the oxygen vacancy movement was obtained by different techniques, in particular, by the thermally stimulated depolarization current measurements for Hf 0.5 Zr 0.5 O 2 , 122 in situ TEM for non-ferroelectric HfO 2 123 and theoretical calculations for ZrO 2 . 184 The values of E a were found to be ∼1.2 and 0.7 eV for singly and doubly charged oxygen vacancies, respectively. As for the wake-up effect at standard conditions, Fengler et al 122 reported a negligible diffusion of oxygen vacancies in the pristine Hf 0.5 Zr 0.5 O 2 film.…”