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Abstract
The exact composition and structure of conductive filaments in hafnia-based memristors are still not fully understood, but recent theoretical investigations reveal that hexagonal HfOx phases close to the h.c.p. Hf structure are probable filament candidates. In this work we list h.c.p. Hf, Hf6O, Hf3O and Hf2O as possible phases for the filament in hafnia memristors. Their differences in lattice parameters, electronic structures and O charge states are studied in details. Migration of O ions for both in-plane and out-of-plane directions in these phases is investigated using first-principles calculations. Both single-phase supercells and filament-in-dielectric models are used for migration barrier calculations, while the latter is proven to be more accurate for the c-direction. The migration of O ions is fastest in metal Hf, while slowest in Hf2O. The existence of O interstitials in Hf tends to hinder the transport of O.
Highlights
Binary oxide-based memristors1,2 that demonstrate stable resistive switching phenomenon3,4 are considered as promising candidates for next-generation non-volatile memory in microelectronics
In this case the movement of O anions and the formation of oxygen-deficient conductive filaments (CFs) are the common features that account for their resistive switching, but the exact composition of the CF is specific to each memristor material
Bader charge calculation confirms that the O interstitials in these phases are in perfect O2- anion form, which precludes the possible existence of neutral O atoms inside metal Hf
Summary
Binary oxide-based memristors that demonstrate stable resistive switching phenomenon are considered as promising candidates for next-generation non-volatile memory in microelectronics. More attention has been paid to HfOx, TaOx, TiOx and AlOx, due to their excellent technical compatibility to CMOS flow-line When active electrodes such as Ag and Cu are not involved, their resistive switching phenomena belong to the valence change mechanism.. The Magnéli phase crystal TinO2n-1 has been identified as the CF structure in TiOx-based memristors, while for TaOx memristors the CF composition was found to be TaO1-x,17 and probably amorphous.. The Magnéli phase crystal TinO2n-1 has been identified as the CF structure in TiOx-based memristors, while for TaOx memristors the CF composition was found to be TaO1-x,17 and probably amorphous.18 When it comes to HfOx, which has been intensively studied as a very promising and reliable memristor material, the exact CF composition is less known. It is still a challenging task to directly identify the CF composition and structure of HfOx-memristors from transmission electron microscopy and scanning tunneling microscopy.
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