The transport properties of oxygen vacancy-related polaron-like bound state in HfOx

Abstract

The oxygen vacancy-related polaron-like bound state migration in HfOx accounting for the observed transport properties in the high resistance state of resistive switching is investigated by the density functional theory with hybrid functional. The barrier of hopping among the threefold oxygen vacancies is strongly dependent on the direction of motion. Especially, the lowest barrier along the <001> direction is 90 meV, in agreement with the experimental value measured from 135 K to room temperature. This hopping mainly invokes the z-directional motion of hafnium and threefold oxygen atoms in the vicinity of the oxygen vacancy resulted from the synergized combination of coupled phonon modes. In the presence of surface, the lowest barrier of hopping between the surface oxygen vacancies is 360 meV along the <101> direction, where the significant surface perpendicular motion of hafnium and twofold oxygen atoms surrounding the oxygen vacancy is identified to facilitate this type of polaron-like bound state migration. Thus, the migration on the surfaces could be more important at the high temperature.

Transition metal attenuated mechanism for protective alumina formation from first principles

“…35) in which cations are taken as polaron trapping sites, and m-HfO 2 (ref. 36) where oxygen vacancies are taken as polaron sites. In the present work we employ the thermally activated hopping approach developed by Marcus, 30 where either fV…”

Sub-band transport mechanism and switching properties for resistive switching nonvolatile memories with structure of silver/aluminum oxide/p-type silicon

“…3 Among many kinds of switching dielectrics, Al x O y based RS-NVM is one of the most promising candidates for the practical application because of their excellent properties and compatibility with CMOS processing. 4,5 The switching mechanisms for most RS-NVMs can be classified into metal-filament type, 6 vacancy-migration type, 7 and interface-barrier-modulate type. 8 These mechanisms have been reported widely for Al x O y based RS-NVM.…”

On the Atomic Kinetic Energies in Ceramic Oxides

“…It may be noted that the heavier the element, the larger part it shares in the low phonon states while on going to higher phonon states the situation reverses. Here too, the silica behaves differently, where along the low frequency phonons, up to ~400 cm [28] titania [29] (rutile) and hafnia [3]. Figure 2.…”

“…Figure 2. Ratio between the simulated VDOS of the X element (X = Si, Ti, Hf) and of the oxygen atom in α-silica [28] (blue), titania (rutile) [29] (red) and hafnia [3] (green). The discontinuity between 800 and 1020 cm −1 in silica is due to the fact that no modes occur along this energy band (see Figure 1).…”

“…This switching phenomenon is not yet fully understood and is speculated to be governed by percolation of oxygen vacancies [2]. Understanding the hoping mechanism of the O-atoms between surface oxygen vacancies in HfO 2 involves the study of hafnia PVDOS [3]. Another exemplifying case is that of amorphous silica (α-SiO 2 ) which is widely used in semiconductor devices and optical fibers.…”