Theoretical Study of Ag Interactions in Amorphous Silica RRAM Devices

In this study, Density Functional Theory (DFT) calculations were used to model the incorporation and diffusion of Ag in Ag/a-Si02/Pt resistive random-access memory (RRAM) devices. The Ag clustering mechanism is vital for understanding device operation and at this stage is unknown. In this paper an O vacancy (Vo) mediated cluster model is presented, where the Vo is identified as the principle site for $\mathrm{Ag}^{+}$ reduction. The $\mathrm{Ag}^{+}$ interstitial is energetically favored at the Fermi energies of Ag and Pt, indicating that $\mathrm{Ag}^{+}$ ions are not reduced at the Pt electrode via electron tunneling. Instead, $\mathrm{Ag}^{+}$ ions bind to Vo forming the $[\mathrm{Ag}/\mathrm{Vo}]^{+}$ complex, reducing $\mathrm{Ag}^{+}$ via charge transfer from the Si atoms in the vacancy. The $[\mathrm{Ag}/\mathrm{Vo}]^{+}$ complex is then able to trap an electron forming $[\mathrm{Ag}/\mathrm{Vo}]^{0}$ at the Fermi energy of Pt. This complex is then able to act as a nucleation site for of Ag clustering with the formation of $[\mathrm{Ag}2/\mathrm{Vo}]^{+}$ which is reduced by the above mechanism.