Theoretical Study of Ag Interactions in Amorphous Silica RRAM Devices

Abstract

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.