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Title: Probing the resistance switching mechanisms in SiOx/Ag RRAM devices
Author: Ibrahim, Sherif
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2020
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Resistive random access memory (RRAM) devices represent promising candidates for emerging non-volatile data storage applications and neuromorphic computing. In those devices, the resistance of a dielectric -often a binary oxide- is switched between a low resistance state (LRS) and one or more high resistance states (HRS) by the application of an appropriate external electrical bias. This resistance switching could be filamentary, i.e., involves the formation of a conductive filament. This filament can be thought of as chains of conductive oxygen vacancies (intrinsic resistance switching) or metallic atoms from an active device electrode (extrinsic resistance switching). In this thesis, the relationship between device electrode material and its resistance switching mechanism in SiOx (x∼1.9)-based RRAM devices was studied. Although it’s widely reported that RRAM devices with electrochemically active top electrodes, such as Ag, switch extrinsically, I show that both mechanisms and their associated conductive filaments can be triggered during device switching in ambient conditions. Resistance vs temperature measurements and conduction mechanism analysis were used to probe the nature of the formed filaments within device oxide layer. Results show that the two mechanisms can coexist within the device during switching. The type of filament generated by the initial electroforming of the device, however, depends on the polarity of the applied voltage during the electroforming step. This finding could help in optimising those RRAM devices for the different storage applications. Although the two mechanisms were observed under ambient conditions, SiOx/Ag devices showed extrinsic switching behaviour only under vacuum. In such an oxygen-poor environment, the contribution of intrinsic resistance switching mechanism appears to be reduced or probably eliminated. In extrinsically electroformed RRAM devices with Ag top electrodes, a metallic filament is likely to form within the switching layer. Using conductance tomography technique, the metallic filament of those SiOx/Ag devices was partially imaged using a conductive AFM (CAFM) tip.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available