Resumen de An oxygen vacancy mediated Ag reduction and nucleation mechanism in SiO2 RRAM devices
K. Patel, J. Cottom, Michel Bosman, A.J. Kenyon, Alexander L. Shluger
Density Functional Theory (DFT) calculations were used to model the incorporation and diffusion of Ag in Ag/SiO2/Me (Me = W or Pt) resistive random-access memory (RRAM) devices. We consider an O vacancy (VO) mediated model of the initial stages of Ag clustering, where the VO is identified as the principle site for Ag+ reduction. The Ag+ interstitial is calculated to be energetically favoured inside a-SiO2 at the Fermi energies of Ag, W and Pt. The adiabatic diffusion barriers of Ag+ are found to be lower than those for Ag0 with a strong dependence on the local network structure, supporting Ag+ being the mobile species during device operation. Ag+ ions bind to VO forming the [Ag/VO]+ complex. The [Ag/VO]+ complex is then reduced by trapping an electron forming [Ag/VO]0. By sampling every VO in a 216-atom cell of a-SiO2 we demonstrate that this mechanism can occur only at 33%, 33% and 11% of O vacancies at the Ag, W and Pt electrodes, respectively. This complex can subsequently act as a nucleation site for Ag clustering with the formation of [Ag2/VO]+, which is reduced by trapping an extra electron.
