TY  - THES
AU  - Skaja, Katharina
TI  - Redox processes and ionic transport in resistive switching binary metal oxides
VL  - 49
PB  - RWTH Aachen
VL  - Dr.
CY  - Jülich
M1  - FZJ-2017-04310
SN  - 978-3-95806-236-8
T2  - Schriften des Forschungszentrums Jülich. Reihe Information / Information
SP  - VII, 203 S.
PY  - 2017
N1  - RWTH Aachen, Diss., 2016
AB  - The growing demand for non-volatile memories requires new concepts in data storage and mobile computing, as the existing flash technology runs into a physical scaling limit. One of the promising candidates for future non-volatile memories is Redox-based Resistive Random Access Memory (ReRAM). This memory technology is based on a non-volatile and reversible switching of device resistance with an external stimulus. The reversible resistance change in the memristive device can be attributed to an electro reduction, which takes place in the metal oxide and/or at the metal oxide electrode interface. The formation of ionic defects and their motion are involved in the electrically induced redox processes, which for most metal oxides is correlated to a valence change of metal ions. Within this thesis the microscopic processes in memristive devices are investigated in order to understand the defect configuration and defect motion in metal oxide thin films. Furthermore, the redox processes localized in nanoscale filaments induced by field-driven defect motion has been elucidated. The resistive switching characteristic of Ta$_{2}$O$_{5-x}$ single layers as well as Nb$_{2}$O$_{5-x}$/ Ta$_{2}$O$_{5-x}$ heterostructures has been investigated. It could be demonstrated that the forming voltage of the memristive devices can be modified by different reactive sputtering conditions. During electrical biasing a morphological change with a dendrite-like shape occurs at the top electrode. The formation of this dendrite-like structure at the metal oxide/metal interface, has been correlated to an avalanche discharge induced redox process in the metal oxide. The dendrite-like structure can be assigned to an oxygen deficient amorphous phase of the metal oxide. The predominant defects in TiO$_{2-x}$ are determined by ionic charge compensation at intermediate oxygen partial pressure and dominated by electronic charge compensation at reducing conditions. For Ta$_{2}$O$_{5-x}$ ceramics as well as thin films the electrical conductivity is dominated by ionic charge compensation over the entire investigated oxygen partial pressure range. The formation energy for oxygen vacancies of single crystal/ceramics is comparable to the values of the thin films. At oxidizing conditions the thin films show an enhanced ionic conduction due to an increased concentration of defects at the grain boundaries and an accumulation of the space charges. The equilibration process in TiO$_{2-x}$ single crystals as well as in thin films is dominated by a surface exchange process. The velocity of the equilibration process is influenced by the surface orientation of single crystals. In TiO$_{2-x}$ thin films a two-fold surface exchange process has been identified. As origin of this two-fold process the incorporation or release of a second species such as water was discussed as well as the influence of the texturing of the thin film and the influence of the substrate.
LB  - PUB:(DE-HGF)3 ; PUB:(DE-HGF)11
UR  - https://juser.fz-juelich.de/record/834335
ER  -