Oxygen vacancy filament formation in TiO2: A kinetic Monte Carlo study

Abstract

We report a kinetic Monte Carlo (kMC) investigation of an atomistic model for 3-dimensional structural configurations of TiO 2 memristor, focusing on the oxygen vacancy migration and interaction under an external voltage bias. kMC allows the access of experimental time scales so that the formation of well defined vacancy filaments in thin TiO 2 films can be simulated. The results show that the electric field drives vacancy migration; and vacancy hopping-induced localized electric field plays a key role for the filament evolution. Using the kMC structure of the filaments at different stages of the formation process, electronic density of states (DOS) are calculated by density functional theory. Filament induced gap states are found which gives rise to a transition from insulating behavior to conducting behavior during the filament formation process. By varying kMC simulations parameters, relations between vacancy diffusion, filament formation, and DOS in the TiO 2 thin film are elucidated. V

Relevance of non-equilibrium defect generation processes to resistive switching in TiO2

“…These results provide much needed atomistic models of defect generation processes in metal oxide materials and provide key parameters needed to assess the role they play in resistive switching. 28 More generally, the results are relevant to a far wider range of TiO 2 applications where non-equilibrium electric field driven defect generation may contribute to material degradation, for example, in photocatalysts, dye-sensitized solar cells and electrodes in rechargeable batteries. [30][31][32] ACKNOWLEDGMENTS K.P.M.…”

“…11,[20][21][22][23][24][25][26] However, resistive switching models are also developed considering field driven diffusion of pre-existing defects only, without defect generation. [27][28][29] Experimentally, definitive evidence for one view over the other has proven extremely challenging to obtain, and the uncertainty that remains presents an obstacle to addressing pressing technological issues, such as controlling cycle-to-cycle and device-to-device variability, increasing endurance, and improving reliability.…”

Kinetic simulation of filament growth dynamics in memristive electrochemical metallization devices

“…[21,22,23,24,25,26] Particularly, the redox reactions at the electrodes are important. The related rates of oxidation of metal atoms and reduction of metal ions are assumed to be constants weighted by Arrhenius-like probabilities which depend on the local electric field and therefore on the local potential.…”

“…[20] However, only a few results have been published so far to study resistive switching on a microscopic scale. [21,22,23,24,25] All the investigations are mainly focusing on initial filament growth rather than on complete formation and dissolutions cycles. Recently, Menzel et al reported on results from two-dimensional kinetic MonteCarlo simulations which allow for several leading physical and chemical processes underlying resistive switching in electrochemical metallization cells.…”

Evaluation of Temperature Stability of Trilayer Resistive Memories Using Work-Function Tuning

“…12) Furthermore, a similar resistance 10 6 -10 8 cm resistivity and a negative temperature coefficient were also reported in the defective silicon, 12) suggesting that the switching behavior in LRS is related to electron hopping via defects. The hopping conduction has been proposed for resistive switching and also demonstrated in reported RRAMs using defective dielectrics including AlO x , 23) ZnO, 24) WO x , 25) TiO x , 26,27) TaO x , 28) ion-doped ZrO 2 , 29) and stacked HfO x /AlO x . 30) The switching mechanism can be explained as follows.…”