An oxygen vacancy mediated Ag reduction and nucleation mechanism in SiO2 RRAM devices. (July 2019)

• Record Type: Journal Article
• Authors: Patel, K.; Cottom, J.; Bosman, M.; Kenyon, A.J.; Shluger, A.L.
• Is Part Of: Microelectronics and reliability. Volume 98(2019)
• Page Start: 144
• Page End: 152
• Publication Date: 2019-07
• Subjects: Electronic apparatus and appliances -- Reliability -- Periodicals; Miniature electronic equipment -- Periodicals; Appareils électroniques -- Fiabilité -- Périodiques; Équipement électronique miniaturisé -- Périodiques; Electronic apparatus and appliances -- Reliability; Miniature electronic equipment; Periodicals; 621.3815
• DOI: 10.1016/j.microrel.2019.05.005
• Languages: English
• ISSNs: 0026-2714

Abstract

Abstract: 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 Ag 0 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. Highlights: The diffusion barriers for Ag + are lower than Ag 0 for a given ring size in a-SiO2 . Ag + is lowest energy charge state at the Fermi energies of Ag, W and Pt. Ag + binds to O vacancies forming [Ag/VO ] + which trap an electron to form [Ag/VO ] 0 . Ag + binding to [Ag/VO ] 0 forming [Agi /VO ] complexes is thermodynamically favourable. 33%, 33% and 11% of vacancies trap and reduce Ag + at the Ag, W and Pt electrodes.